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Twin Peaks: more twinning in humans than ever before

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STUDY QUESTION How many twins are born in human populations and how has this changed over recent decades? SUMMARY ANSWER Since the 1980s, the global twinning rate has increased by a third, from 9.1 to 12.0 twin deliveries per 1000 deliveries, to about 1.6 million twin pairs each year. WHAT IS KNOWN ALREADY It was already known that in the 1980s natural twinning rates were low in (East) Asia and South America, at an intermediate level in Europe and North America, and high in many African countries. It was also known that in recent decades, twinning rates have been increasing in the wealthier parts of our world as a result of the rise in medically assisted reproduction (MAR) and delayed childbearing. STUDY DESIGN, SIZE, DURATION We have brought together all information on national twinning rates available from statistical offices, demographic research institutes, individual survey data and the medical literature for the 1980–1985 and the 2010–2015 periods. PARTICIPANTS/MATERIALS, SETTING, METHODS For 165 countries, covering over 99% of the global population, we were able to collect or estimate twinning rates for the 2010–2015 period. For 112 countries, we were also able to obtain twinning rates for 1980–1985. MAIN RESULTS AND THE ROLE OF CHANCE Substantial increases in twinning rates were observed in many countries in Europe, North America and Asia. For 74 out of 112 countries the increase was more than 10%. Africa is still the continent with highest twinning rates, but Europe, North America and Oceania are catching up rapidly. Asia and Africa are currently home to 80% of all twin deliveries in the world. LIMITATIONS, REASONS FOR CAUTION For some countries, data were derived from reports and papers based on hospital registrations which are less representative for the country as a whole than data based on public administrations and national surveys. WIDER IMPLICATIONS OF THE FINDINGS The absolute and relative number of twins for the world as a whole is peaking at an unprecedented level. An important reason for this is the tremendous increase in medically assisted reproduction in recent decades. This is highly relevant, as twin deliveries are associated with higher infant and child mortality rates and increased complications for mother and child during pregnancy and during and after delivery. STUDY FUNDING/COMPETING INTEREST(S) The contribution of CM was partially supported by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant No 681546, FAMSIZEMATTERS), Nuffield College, and the Leverhulme Trust. The contribution of GP was partially supported by the French Agence Nationale de la Recherche (grant No ANR-18-CE36-0007-07). The authors declare no conflict of interest. TRIAL REGISTRATION NUMBER N/A.
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Twin Peaks: more twinning in humans than ever before
Christiaan Monden, Gilles Pison, Jeroen Smits
To cite this version:
Christiaan Monden, Gilles Pison, Jeroen Smits. Twin Peaks: more twinning in humans than ever
before. Human Reproduction, 2021, pp.1-8. �10.1093/humrep/deab029�. �hal-03169231�
Twin Peaks: more twinning in humans
than ever before
Christiaan Monden
1,2,3
, Gilles Pison
4,5
, and Jeroen Smits
6
*
1
University of Oxford, OX1 2JD Oxford, UK
2
Nuffield College, OX1 1NF Oxford, UK
3
Leverhulme Centre for Demographic Science,
OX1 1JD Oxford, UK
4
French Institute for Demographic Studies (INED), 75980 Paris, France
5
French Museum of Natural History
(UMR 7206), 75005 Paris, France
6
Global Data Lab, Institute for Management Research, Radboud University, 6525 XZ Nijmegen,
the Netherlands
*Correspondence address: Jeroen Smits, Global Data Lab, Institute for Management Research, Radboud University, PO Box 9108,
6500HK Nijmegen, the Netherlands. E-mail: j.smits@fm.ru.nl
Submitted on June 4, 2020; resubmitted on January 18, 2021; editorial decision on January 25, 2021
STUDY QUESTION: How many twins are born in human populations and how has this changed over recent decades?
SUMMARY ANSWER: Since the 1980s, the global twinning rate has increased by a third, from 9.1 to 12.0 twin deliveries per 1000 de-
liveries, to about 1.6 million twin pairs each year.
WHAT IS KNOWN ALREADY: It was already known that in the 1980s natural twinning rates were low in (East) Asia and South
America, at an intermediate level in Europe and North America, and high in many African countries. It was also known that in recent deca-
des, twinning rates have been increasing in the wealthier parts of our world as a result of the rise in medically assisted reproduction
(MAR) and delayed childbearing.
STUDY DESIGN, SIZE, DURATION: We have brought together all information on national twinning rates available from statistical offi-
ces, demographic research institutes, individual survey data and the medical literature for the 1980–1985 and the 2010–2015 periods.
PARTICIPANTS/MATERIALS, SETTING, METHODS: For 165 countries, covering over 99% of the global population, we were able
to collect or estimate twinning rates for the 2010–2015 period. For 112 countries, we were also able to obtain twinning rates for 1980–
1985.
MAIN RESULTS AND THE ROLE OF CHANCE: Substantial increases in twinning rates were observed in many countries in Europe,
North America and Asia. For 74 out of 112 countries the increase was more than 10%. Africa is still the continent with highest twinning
rates, but Europe, North America and Oceania are catching up rapidly. Asia and Africa are currently home to 80% of all twin deliveries in
the world.
LIMITATIONS, REASONS FOR CAUTION: For some countries, data were derived from reports and papers based on hospital regis-
trations which are less representative for the country as a whole than data based on public administrations and national surveys.
WIDER IMPLICATIONS OF THE FINDINGS: The absolute and relative number of twins for the world as a whole is peaking at an un-
precedented level. An important reason for this is the tremendous increase in medically assisted reproduction in recent decades. This is
highly relevant, as twin deliveries are associated with higher infant and child mortality rates and increased complications for mother and
child during pregnancy and during and after delivery.
STUDY FUNDING/COMPETING INTEREST(S): The contribution of CM was partially supported by the European Research Council
(ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (grant No 681546, FAMSIZEMATTERS), Nuffield
College, and the Leverhulme Trust. The contribution of GP was partially supported by the French Agence Nationale de la Recherche
(grant No ANR-18-CE36-0007-07). The authors declare no conflict of interest.
TRIAL REGISTRATION NUMBER: N/A.
Key words: multiple pregnancy / world / assisted reproduction / changes over time / twinning
V
CThe Author(s) 2021. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Comme rcial License (http://creativecommons.org/licenses/by-nc/4.0/), which
permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact
journals.permissions@oup.com
Human Reproduction, Vol.00, No.0, pp. 1–8, 2021
doi:10.1093/humrep/deab029
ORIGINAL ARTICLE Reproductive epidemiology
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Introduction
Twins have fascinated scientists (Mackenzie,1841;Duncan, 1865;
Zeleny,1921) and the general public (Segal 2017) for centuries. Part of
this interest is driven by the health implications of twin pregnancies.
Twins have more complications at birth, are more often born
premature, and have lower birth weights and higher still birth and
infant mortality rates (Pison, 1992;Guo and Grummer-Strawn, 1993;
Larroque et al.,2004;Delobel-Ayoub et al., 2009;Monden and Smits,
2017). Also, the risk of complications for the mother, e.g. gestational
diabetes, pre-eclampsia and post-partum depression and maternal
mortality, are substantially increased in twin pregnancies (Bdolah
et al.,2008;Choi et al.,2009;Rauh-Hain et al.,2009;Jena et al., 2011).
It has long been known that the frequency of twin births varies
across populations (Bulmer,1970) as does the treatment and social
status of twins (Eells,1892;Pison, 1992). A first overview of the global
twinning distribution by the end of the 20th century was provided by
Pison (2000) based on rough estimates for low and middle income
countries (LMICs). Given that the situation has been highly dynamic in
recent decades and better data for LMICs have become available
(Smits and Monden, 2011), there is need for a new and truly global
overview of twinning distribution in the world. In this article, such an
overview is provided for the period 2010–2015. In addition, a similar
overview is presented for the period 1980–1985, so that the shifts in
the absolute and relative global twinning distribution over a period of
30 years can be observed.
We already know that, in the 1970s, twinning rates were low in
(East) Asia, at an intermediate level in Europe and North America,
and high in several African countries, where Nigeria was seen as the
twinning champion of the world (Bulmer,1970;Hall, 2003;Hoekstra
et al.,2008). More recently, it was shown that rates were also low in
Central and South America (Go´mez et al.,2019), particularly in coun-
tries with large indigenous populations, and that Nigeria is part of a
broader Central African high twinning zone running from west to east
across the continent (Smits and Monden, 2011). Although the extant
literature suggests some general patterns, it provides a highly frag-
mented picture as most studies concern one or just a few countries,
refer to different years, and ultimately do not cover the majority of
countries.
Since the first records began, twinning rates have been moving with
the tide of marriage age and family size, as older mothers and higher
birth orders are associated with more twins (Duncan,1865;Pison and
D’Addato, 2006). However, the effects of changes in age at birth and
fertility were small to modest compared to the regional differences in
the global pattern of twinning rates (Bulmer,1970;Pison et al.,2015).
Over the last three decades, new medical technologies have become
important determinants of twinning. Medically assisted reproduction
(MAR) has been one of the main drivers of increasing twin rates in
several countries (Imaizumi, 1997;Blondel and Kaminski,2002;
Hoekstra et al.,2008;Martin et al.,2012;Pison et al., 2015;Go´mez
et al.,2019). It is unclear, however, how the rise of MAR on the one
hand and changing demographic behaviour on the other have changed
the absolute and relative number of twins and their distribution around
the globe.
Medically assisted reproduction has increased substantially since the
1970s (Deng et al.,2019;European IVF monitoring Consortium, 2020).
MAR refers to a broader set of treatments other than those known as
assisted reproductive technology (ART), which refers to treatments in
which both sperm and oocyte are handled outside (i.e. in vitro)ofthe
woman’s body and embryos are transferred to establish a pregnancy.
ART includes, but is not limited to, in vitro fertilization (IVF) and its var-
iant, intracytoplasmic sperm injection (ICSI). However MAR also
includes simpler techniques, such as ovarian stimulation and artificial in-
semination. Techniques such as ovarian stimulation and IVF are associ-
ated with increased numbers of multiple births (Nyboer Andersen
et al.,2007;Hoekstra et al.,2008). Most of this increase is in dizygotic
twinning, although there is also evidence for a smaller increase in
monozygotic twinning associated with MAR (Astonet al., 2008).
As the diffusion and large scale use of these techniques varies signifi-
cantly among countries (Collins, 2002;Ferraretti et al., 2017), the
global twinning landscape has likely altered dramatically. Large scale
use of MAR started in the 1970s in the most developed countries,
spread in the 1980s and 1990s to emerging economies in Asia and
Latin America, and reached South Asia and the most wealthy groups
in Africa only after 2000 (Collins, 2002;Inhorn and Patrizio, 2015;
Pison et al.,2015;Botha et al., 2018). Availability and accessibility are
still very low in most low income countries.
We contrast twining rates in 2010–2015, when the influence of
MAR reached a peak (European IVF monitoring Consortium, 2020),
to rates in 1980-1985, when MAR was still at low levels, even in high
income countries, and when genetic differences, overall fertility, age at
childbearing and parity were the major driving factors (Meulemans
et al.,1996;Beemsterboer et al.,2006;Derom et al.,2011). Since the
early 1980s, many countries have seen significant changes in age at
birth and parity distributions. There is evidence, at least for some
countries, that the natural twinning rate (i.e. excluding births after
MAR) remained stable (Derom et al., 2011) and that increases in the
total twinning rate were driven by the combination of changing age
at birth and MAR (Pison et al., 2015). Imaizumi’s (1997) analysis of
10 countries shows that until 1980 there is no clear effect of MAR on
twin rates.
We have systematically brought together information on national
twinning rates for 165 countries, covering over 99% of the global
population, for the 2010–2015 period. For 112 countries, we were
also able to measure or estimate a twinning rate for 1980–1985. This
new database allows us to present a comprehensive global overview
of twinning rates and assess how the global distribution of twinning has
changed over three decades.
Materials and methods
Materials
Data on twin deliveries for 165 countries or territories were brought
together into a new database called the Human Multiple Births
Database (HMBD; https://www.twinbirths.org/), which aims to bring
together all available information on twin deliveries at the national level
across the globe. For countries which have reliable statistics on births
by multiplicity that are based on complete or nearly complete civil reg-
istration (mostly developed countries and a few developing countries),
data derived from vital statistics systems of national statistical offices
were used. For the first period, we used the mean of the available
2Monden et al.
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data for the years 1980–1985 and for the second period, we used the
mean of the available data for 2010–2015.
For countries for which vital statistics on births by multiplicity are
missing or not reliable, the HMBD includes twin deliveries derived
from published sources or computed on the basis of household sur-
veys that include birth histories of women. Since the 1960s, many na-
tional representative household surveys have been held in LMICs that
include information on twin deliveries. For the current article, twin
rates were used from well-established large-scale survey programs: the
Demographic and Health Surveys (https://www.dhsprogram.com/)
and UNICEF’s Multiple Indicator Cluster Surveys (mics.unicef.org).
Data from these surveys programs are routinely employed by national
and international institutions (World Bank, UNDP) to document the
socio-demographic and health characteristics of LMICs.
The group of countries for which survey data are used can be sub-
divided into countries where the use of MAR in the period 1980–2010
was negligible and countries for which some influence of MAR can be
expected. All sub-Saharan African countries belong to the first group
(Botha et al.,2018;Dyer et al., 2020). For these countries, little
change in twinning rates was expected as MAR was only available to a
very small elite. These countries do not have reliably sources for direct
measures for 1980–1985. We use births in the 2000–2009 period to
estimate twin rates for the earlier period and assume that the twin
rate has not changed significantly since 1980–1985. Supplementary
Figure S2 shows that this is a reasonable assumption for births since
1990. There is no evidence for an increase in the twin rate across
sub-Saharan Africa in the DHS starting in the 1990s.
The second group of countries for which no reliable vital statistics
are available and hence survey data are used, includes countries in
Latin America, parts of Asia and the MENA region (Middle East and
North Africa). These countries were wealthy enough during the period
under study to expect some influence of MAR. For these countries,
we estimated figures for the 1980–1985 period with retrospective in-
formation from surveys held between 1987 and 1995 on births that
occurred in the 10 years before these surveys. For the second period,
we used information from surveys held after 2009 on births that oc-
curred between 2010 and 2015.
For some countries, we derived twin rates from published sources,
like journal articles or demographic reports. Data derived from these
sources vary in quality depending on the kind of data on which they
are based (e.g. national representative data or hospital based surveys).
We only used reports where the data sources were clearly described
and could be reasonable taken as nationally representative.
The twinning rate is defined as the proportion of twin deliveries out
of the total number of deliveries, expressed per 1000 deliveries. Most,
but not all, of the variation in twinning rates observed in this study
reflects variation in dizygotic twinning, as monozygotic twinning rates
are about 4 per 1000 deliveries everywhere in the world
(Bulmer,1970;Bortolus et al., 1999). All rates and their sources are
available in Supplementary Tables SII and SIII and can be downloaded
from https://www.twinbirths.org/.
Methods
In a first step, we determined the absolute number of twin deliveries
and the total number of deliveries in a particular year for each country,
including those for which reliable vital statistics on births are missing.
We used the total number of deliveries in the country, as estimated
by the United Nations (2017), and the twinning rate, as we estimated
it, and apply the formula below.
We define
a¼total number of births
b¼twinning rate (expressed as a proportion)
c¼number of twin deliveries
d¼total number of deliveries
We obtain afrom the UN World Population Prospects and bfrom
our own calculations. We then calculate c¼a*b/(1þb)andd¼a
c.
In a second step, we calculated the absolute and relative number of
twin deliveries for groups of countries (regions, continents), and for
the whole world, by summing the absolute number of twin deliveries
and the total number of deliveries of each country. We are then able
to calculate the twinning rate for groups of countries, or for the whole
world, by dividing the number of twin deliveries by the total number
of deliveries.
When we calculate the number of twin deliveries for a whole group
of countries, but no estimate for the twinning rate for a particular
country of this group is available, we suppose that the twinning rate in
this country is equal to that one for their whole group computed on
the basis of countries for which we do know the twinning rate.
Further details of the total number of deliveries, the number of twin
deliveries, and the proportion of twin deliveries for each country are
provided in Supplementary Tables SI,SII and SIII.
Results
Figure 1 depicts the distribution of twinning rates for 2010–2015,
Supplementary Fig. S1 depicts the distribution of twinning rates for
1980–1985, and Fig. 2 depicts the change in twinning rates between
1980–1985 and 2010–2015. In both periods, Africa had the highest
twinning rates and, for this continent, no significant increase between
the two periods was observed. On the other hand, the high rates
observed in the 2010–2015 period in, for example, Greece, Denmark
and South Korea, are the result of rapid increases in the twinning rates
between the two periods.
Substantial increases in twinning rates, even doubling or more, could
be seen in many other countries in Europe, North America and (East)
Asia. Except for the poorest countries in Africa and South Asia and a
number of countries in Central and South America, the majority of
countries showed a substantial increase in twinning rates. For 74 of
112 countries, we observed an increase of more than 10% whereas a
decrease of more than 10% was found in only seven countries. For
most countries, the current proportion of twin deliveries has never
been higher since records began.
At the regional level, increases in twinning rates and a shift in the
distribution of twins is also evident. Table 1 presents twinning rates for
the world as a whole and for major regions in the two time periods.
Apart from Africa and South America, where twinning rates have
remained nearly unchanged, all regions show substantial increases,
ranging from 32% in Asia to 71% in North America (Fig. 3). The abso-
lute number of twin deliveries has increased everywhere except in
South America. In North America and Africa, the absolute number of
More twinning in humans than ever before 3
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twin deliveries has increased by more than 80%. In Africa, this increase
is almost entirely caused by population growth.
The figures make clear that changes over the last three decades
have altered the global twinning landscape completely. These changes
were largely driven by reproductive and fertility choices of households,
and were initially concentrated in Europe and North America,
followed by a number of emerging economies in (East) Asia. This re-
markable change in the global pattern has remained hidden in the
highly fragmented information on trends in twinning rates.
It is important to note that the number of children implied by the
twinning rates for 2010–2015 are substantial. For example the North
American twinning rate of 16.9 per 1000 deliveries implies that 3.4%
of all children born in North America in that period were twins. For
Africa the same percentage applies. The twinning rate of 12.0 for the
world as a whole means that one of every 42 children born on earth
is a twin.
Table 1 also shows that Asia and Africa are now home to more
than 80% of the world twin deliveries and share them nearly equally
(42% and 41% respectively). Africa’s share has increased between the
two periods whereas that of Asia’s share has decreased. Africa’s share
of all twin deliveries (42% in 2010–2015) is much higher than its share
of the overall world population (15%; United Nations, 2017) because
of a high birth rate and a high twinning rate. Unfortunately these
African twins still face a very high absolute mortality rate (Monden and
Smits, 2017).
In 2010–2015, the absolute number of twin deliveries was higher
than ever before, at the world level, as well as for all global regions ex-
cept South America, where the absolute number of twin deliveries has
declined slightly. While the global total number of births has increased
by only 8%, the number of twin deliveries has increased by 42%
(Fig. 3). By 2010–2015, more than 1.6 million sets of twins were born
every year. This increase will become even more visible among
(young) adults as lower mortality means that more twin pairs than
ever before will survive until adulthood. In 2010–2015, about 2.4% of
all newborns was a twin child.
The sharp increase in twinning rates in Europe and Asia has resulted
in a seemingly counterintuitive finding: while there were fewer deliver-
ies in these two regions in 2010–2015 than in 1980–1985, there were
more twin deliveries in the later period, as Fig. 3 illustrates.
Supplementary Table SI provides similar information as Table 1,but
is based on the more detailed Geographic Regions of the United
Nations Statistic Division (https://unstats.un.org/unsd/methodology/
m49/). This table shows that in Europe, the changes in twinning rates
were smaller in the East European countries than in the other parts of
the continent. In Asia, the largest changes have taken place in the West
Asian and East Asian countries, while South Asia and South-East Asia
Figure 1. Twin deliveries per 1000 total deliveries in 2010–2015.
4Monden et al.
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still lag behind. In Africa, the North African and particularly South
African countries have been catching up with the West African and
Central African countries, which in 1980–1985 still had the highest twin-
ning rates in the world. In the Central and South American region, the
more dynamic changes can be observed in the Caribbean and Central
American countries, whereas South America showed hardly any change.
Our study also shows that differences in the proportion of twin de-
liveries between countries and regions have diminished between
Figure 2. Percentage change in twin deliveries per 1000 deliveries between 1980–1985 and 2010–2015.
................................................................................................................................................................................................. ...........................
Table 1 Absolute and relative number of twin and all deliveries, in the world and by region, in 1980–1985 and 2010–2015.
Number of
twin deliveries
(thousands)
Share of all
twin deliveries
in the world
Total number of
deliveries (thousands)
Share of all
deliveries in the world
Twinning rate
(twin deliveries per 1000)
1980–1985 2010–2015 1980–1985 2010–2015 1980–1985 2010–2015 1980–1985 2010–2015 1980–1985 2010–2015
Africa 373 674 32% 41% 22,684 39,559 18% 29% 16.5 17.1
Asia 556 693 48% 42% 80,006 75,435 62% 54% 7.0 9.2
Europe 90 113 8% 7% 9,944 7,878 8% 6% 9.1 14.4
North America 38 71 3% 4% 3,937 4,251 3% 3% 9.9 16.9
Oceania 4 9 0% 1% 481 640 0% 0% 10.1 14.8
South America 102 100 9% 6% 11,772 10,823 9% 8% 8.7 9.3
World 1,165 1,663 100% 100% 128,827 138,590 100% 100% 9.1 12.0
Notes: Own calculations.
More twinning in humans than ever before 5
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1980–1985 and 2010–2015. We observed a convergence towards
high twinning rates in almost all regions.
Discussion
We have brought together all available statistical information on the
frequency of twin births across the globe, to document the variation in
twinning rates among countries and how this variation has changed
since the 1980s. Our results show that twinning rates were recently
peaking at a historical high, with rates of over 15 twin deliveries per
1000 deliveries in many countries, including the USA, Canada, the
European Union, Israel, South Korea, Taiwan, and almost all African
countries. Only the poorer regions of Latin America and in South and
South-East Asia had lower twinning rates, often (well) below 10 twin
deliveries per 1000 deliveries.
We compared our recent twinning map with an earlier map, which
we constructed on the basis of data for the first part of the 1980s,
when twinning rates were still almost completely ‘natural’ in terms of
the effects of MAR. This comparison revealed a huge rise in the global
twinning rate, which increased by a third, from 9.1 to 12.0 twin deliv-
eries per 1000 deliveries, in only three decades.
Also the distribution of twinning rates across the globe has changed
considerably during this period. In the 1980s, global twinning rates
were still largely dominated by high twinning rates in sub-Saharan Africa
and moderate rates in North America and Europe. In the other areas
of the globe, the rates were low at that time, often only slightly above
the bottom line represented by the monozygotic twinning rate, which
is about 4 twin pairs per 1000 deliveries everywhere in the world.
There is broad evidence that the enormous change in the global
twinning rate is to a large extent caused by the increased use of
MAR, which started in the wealthier regions of our world in
the 1970s, spread to emerging economies in Asia and Latin America
in the 1980s and 1990s, and reached the more prosperous sub-
populations of South Asia and Africa only after 2000 (Imaizumi,
1997;Mills et al., 2014;Inhorn and Patrizio, 2015;Botha et al.,
2018). While the important role of MAR is undisputed, also the
increasing age at birth has contributed to increased twinning rates in
high income countries.
According to Pison et al. (2015), the effect of MAR is on average
about three times larger than the effect of delayed childbearing.
However, there are substantial differences between countries. In
Spain, Greece and Singapore, the effect of MAR is five to six times
greater than that of delayed childbearing; in the United States, Canada
and Switzerland it is three to four times greater, In France, Germany
and Sweden it is about two times greater, and in Finland, Hungary and
New Zealand the effects of both factors are about similar (Pison et al.,
2015). Besides MAR and delayed childbearing, also other factors may
have contributed to the change, although no convincing evidence has
been documented yet.
The strong increase in number of twin births due to MAR started
to raise concerns in the 1990s among medical authorities and policy
makers, because of the public health problems related to twin births.
Twins are a high-risk group associated with complications during preg-
nancy, at birth and thereafter, including preterm deliveries, lower birth
weight, increased still births and infant and maternal mortality (Bdolah
et al.,2008;Choi et al.,2009;Delobel-Ayoub et al.,2009;Jena et al.,
2011;Monden and Smits,2017).
Because of these concerns, many developed countries started to
change their MAR regulations and clinical practices around 2000
(Mills et al.,2014;Pison et al.,2015), whereby reductions in the
number of transferred embryos were implemented and the focus
was directed towards the successful live birth delivery of singletons.
It therefore is possible that, in these countries, the twinning rates
observed for the 2010–2015 period are at an all-time high and the
rates might start to decrease in the coming decade. In Europe, the
number of transfers of a unique embryo in IVF/ICSI (during fresh
cycles) was barely higher than 10% in the late 1990s, but has since
increased continuously to just above 40% in 2017. The number of
transfers involving two embryos has been fluctuating around 55%,
while transfers of three or more have declined steadily (European
IVF monitoring Consortium, 2020).
In line with these developments, in some of the most developed
countries, twinning rates were found to plateau in the early 2000s
(Pison et al., 2015). However, in many other countries, no such pat-
tern was observed, so it remains to be seen whether a reversal of the
trend will actually take place. From a global perspective, the changes in
these developed countries might easily be counterbalanced by devel-
opments in the highly populated South and South-East Asian countries,
where the diffusion and growth of MAR in combination with still very
low twinning rates might lead to a substantial increase in both twinning
rates and absolute numbers of twins. These regions are likely to see
further increases in age at birth too. This is another important factor
that contributes to higher twinning rates.
For sub-Saharan Africa, which so far has not seen a strong increase
in twinning rates, it remains an open question what the net effect will
be of the combination of lower overall fertility, higher age at birth, and
higher uptake of MAR. While the first development would reduce
twinning rates, the latter two would lead to higher levels of twinning.
Some limitations need to be considered when interpreting our find-
ings. One limitation concerns the quality of the data. For most devel-
oped countries, twin rates were obtained from statistical offices or
national medical registrations, which are generally of high quality. For
LMICs, in many cases representative household surveys with complete
Figure 3. Change in number of total births, twin births
and twinning rate from 1980–1985 to 2010–2015 by region.
6Monden et al.
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birth histories were available, which are of reasonable quality (reflected
in relatively low within-country variation between surveys held in dif-
ferent years (Monden and Smits, 2017)). For the 2010–2015 twin
rates of China and Saudi-Arabia, we had to rely on published reports.
While the Chinese data are of high quality and are nationally represen-
tative, the Saudi data come from one single hospital and therefore
need to be treated as an estimate with considerable uncertainty. The
twin rate may be overestimated if women pregnant with twins are
more likely to deliver in this hospital rather than elsewhere compared
to women pregnant with a singleton.
Unfortunately, we have not been able to produce a comprehensive
overview of the situation before 1980. Nationally representative infor-
mation on twinning rates is increasingly scarce for earlier periods, es-
pecially for LMICs. However, some of the main geographical
differences in the 1980–1885 overview are in line, certainly in rank or-
der, with evidence based on smaller studies from the mid or early
20th century, such as those collected by Bulmer (1970) in his seminal
book. The main pattern of high twinning in Africa, low twinning in Asia
and intermediate levels in Europe are generally thought to stem from
genetic differences, while changes within the regions are driven by ma-
ternal age, fecundity and voluntary birth control (Bulmer, 1970;
Imaizumi, 1997;Pison and Couvert, 2004).
In many countries, reliable statistics on MAR are still lacking. We
should also bear in mind that substantial numbers of women travel to
other countries for fertility treatments (Shenfield et al., 2010;Mills et
al., 2014). It is unclear at the moment, how this may affect the twin
rate in their country of residence. This might be particularly relevant
for richer urban elites in emerging economies, for whom we still rely
on survey data rather than vital register or census data. Accurate and
detailed data on twin rates are also important for forecasting the de-
mand for health services given the health implications for twins and
their mothers. This is particularly important in low-income countries,
where mortality among twins is highest and care for women expecting
twins is often inadequate by modern standards (Monden and Smits,
2017). Improved registration and monitoring of twin births would
help target these health issues. More generally, it would allow us to
better understand the cultural, political and economic factors that con-
tribute to differences in twin rates not only between but also within
countries.
Supplementary data
Supplementary data are available at Human Reproduction Online.
Data availability
All data are available in the article and supplementary materials.
Acknowledgements
Many named and unnamed employees of National Bureaus of Statistics
and Ministries of Health from countries around the world kindly
responded to requests for data.
Authors’ roles
All authors contributed substantially and equally to the conception, de-
sign, data acquisition and drafting of the article.
Funding
The contribution of CM was partially supported by the European
Research Council (ERC) under the European Union’s Horizon 2020
Research and Innovation Programme (grant No 681546,
FAMSIZEMATTERS), Nuffield College, and the Leverhulme Trust. The
contribution of GP was partially supported by the French Agence
Nationale de la Recherche (grant No ANR-18-CE36-0007-07).
Conflict of interest
The authors declare no conflict of interest.
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Background Twins and late preterm (LPT) infants are at an increased risk of being breastfed to a lesser extent than term singletons. This study aimed to describe the initiation and duration of any and exclusive breastfeeding at the breast for mothers of LPT twins and term twins during the first 4 months and to explore the breastfeeding experiences of mothers of LPT twins. Methods A sequential two-sample quantitative–qualitative explanatory mixed-methods design was used. The quantitative data were derived from a longitudinal cohort study in which 22 mothers of LPT twins and 41 mothers of term twins answered questionnaires at one and four months after birth (2015–2017). The qualitative data were obtained from semi-structured interviews with 14 mothers of LPT twins (2020–2021), based on results from the quantitative study and literature. Analysis included descriptive statistics of quantitative data and deductive content analysis of the qualitative data, followed by condensation and synthesis. Results All mothers of LPT twins (100%) and most mothers of term twins (96%) initiated breastfeeding. There was no difference in any breastfeeding during the first week at home (98% versus 95%) and at 1 month (88% versus 85%). However, at 4 months, the difference was significant (44% versus 75%). The qualitative data highlighted that mothers of LPT twins experienced breastfeeding as complex and strenuous. Key factors influencing mothers’ experiences and decisions were their infants’ immature breastfeeding behaviors requiring them to express breast milk alongside breastfeeding, the burden of following task-oriented feeding regimes, and the lack of guidance from healthcare professionals. As a result, mothers started to question the worth of their breastfeeding efforts, leading to changes in breastfeeding management with diverse results. Support from fathers and grandparents positively influenced sustained breastfeeding. Conclusions Mothers of LPT twins want to breastfeed, but they face many challenges in breastfeeding during the first month, leading to more LPT twins’ mothers than term twins’ mothers ceasing breastfeeding during the following months. To promote and safeguard breastfeeding in this vulnerable group, care must be differentiated from routine term infant services, and healthcare professionals need to receive proper education and training.
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Fetal growth restriction contributes to the excess perinatal mortality and morbidity associated with twin pregnancies. Regular ultrasound monitoring for fetal growth restriction is an essential component of antenatal care of twin gestations. It is accepted that twins have divergent growth trajectories around 28-30 weeks’ gestation and are born smaller compared to singletons. Despite this well-established difference in fetal growth, twin pregnancies have been traditionally managed using growth standards developed for singleton pregnancies. Numerous recent studies have demonstrated a strong case supporting the use of twin-specific growth standards, but clinical implementation has been lacking. In this paper, we will review the evidence on factors affecting fetal growth, the rationale for twin-specific reference charts, clinical evidence for their use, and future direction of research. Applying singleton growth standards to twin pregnancies inflates the abnormal growth rate and recent clinical evidence from several studies suggests that they are too stringent for classification of twins. The association of adverse perinatal and maternal outcomes such as perinatal death, preterm birth, neonatal care unit admission, hypertensive disorders of pregnancy, and composite neonatal morbidity is stronger when classification is made using twin-specific standards compared to singletons.
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The number of twin births varies from region to region. However, they show different values not only based on territory but also on other characteristics, such as demographics, genetics, and biological factors. In general, we know from the literature and research that the combined effect of biological or natural factors and/or the artificial treatments also increases the chances of twin conceptions and twin births. While in OECD countries, one in fifty births occurred in the 1960s and 1970s, by the mid-1990s, one in thirty births was twins. Around 2010–2012, the frequency reached the level where one twin birth appeared after every 25 births, while in 2018 the estimated rate was 28 worldwide.
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Dieser Beitrag bietet eine umfassende Einführung in den Themenkomplex Infertilität, Reproduktionsmedizin und Familie. Neben der Definition zentraler Begriffe wird der inhaltliche Fokus auf die Ursachen der Nutzung von Reproduktionsmedizin und die zugrunde liegenden rechtlichen und finanziellen Rahmenbedingungen gelegt. Zusätzlich werden die Determinanten der Nutzung, aber auch die Auswirkungen reproduktionsmedizinischer Behandlungen für Familien und Kinder genauer betrachtet. Eine Herausforderung ist die aktuelle Datenlage für sozialwissenschaftliche Analysen, die ebenfalls diskutiert wird. Der Beitrag schließt mit einem Ausblick auf zukünftige Forschungsfelder.
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Background: Reducing maternal and perinatal mortality is a global objective. Hong Kong is a city with low maternal and perinatal mortality but little is known about the trend and causes of these deaths in this high-income city. We analyzed the maternal death, stillbirth and neonatal death since 1946 in Hong Kong. Methods: Data were extracted from vital statistics, based on the number of registered deaths and births, provided by the Department of Health, the Government of the HKSAR. The annual change rate of mortality was evaluated by regression analysis. Contextual factors were collected to assess the association with mortality. Findings: Between 1946 and 2017, the stillbirth rate (per 1,000 total births) reduced from 21·5 to 2·4; early and late neonatal deaths (per 1,000 live births) reduced from 14·1 and 18·1 to 0·7 and 0·4 in 2017, respectively. The maternal mortality ratio (per 100,000 live births) declined from 125 to 1·8.The causes of maternal and perinatal deaths were available since 1981 and 1980 respectively. The leading causes of death were thromboembolism (37·0%) and obstetric haemorrhage (30·4%) for maternal death; congenital problem (30·1%) and prematurity (29·0%) for neonatal death. No data on causes of stillbirth were available. No specific shift of pattern was observed in the causes of maternal and neonatal death with time. There were no cases of maternal death due to sepsis and only 2 cases (2·2%) of maternal deaths due to indirect cause. Interpretation: The maternal and perinatal death have reduced significantly in Hong Kong and maintained at the lowest level globally. Indirect maternal death and sepsis were unusual causes of maternal deaths. Use of ICD-PM stillbirth classification, setting up a maternal death confidential enquiry and adding pregnancy checkbox could be the next step to identify and categorize hidden burden. Funding: Nil.
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Background: Group B streptococcal (GBS) infection remains one of the most significant causes of late-onset sepsis and meningitis (LOGBS) among young infants. However, transmission routes and risk factors for LOGBS are not yet fully understood. Methods: We conducted systematic reviews on clinical risk factors previously reported in the literature (prematurity, low birth weight [<2500 g], antenatal colonization, multiple-gestation pregnancy, maternal age <20 years, male infant sex, intrapartum fever, prolonged rupture of membranes) and meta-analyses to determine pooled estimates of risk. Results: We included 27 articles, reporting 5315 cases. Prematurity (odds ratio 5.66; 95% confidence interval [4.43-7.22]), low birth weight (6.73; [4.68-9.67]), maternal colonization (2.67; [2.07-3.45]), and multiple-gestation pregnancies (8.01; [5.19-12.38]) were associated with an increased risk of LOGBS. Conclusions: Prematurity/low birth weight and maternal colonization are major risk factors for LOGBS. Future GBS vaccine studies should try to establish the optimal time for vaccination during pregnancy to protect preterm infants.
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Study question: What are the reported data on cycles in ART, IUI and fertility preservation (FP) interventions in 2016 as compared to previous years, as well as the main trends over the years? Summary answer: The 20th ESHRE report on ART and IUI shows a progressive increase in reported treatment cycle numbers in Europe, with a decrease in the number of transfers with more than one embryo causing a reduction of multiple delivery rates (DR), as well as higher pregnancy rates and DR after frozen embryo replacement (FER) compared to fresh IVF and ICSI cycles, while the outcomes for IUI cycles remained stable. What is known already: Since 1997, ART aggregated data generated by national registries, clinics or professional societies have been collected, analysed by the European IVF-monitoring Consortium (EIM) and reported in 19 manuscripts published in Human Reproduction and Human Reproduction Open. Study design size duration: Yearly collection of European medically assisted reproduction (MAR) data by EIM for ESHRE. The data on treatments performed between 1 January and 31 December 2016 in 40 European countries were provided by either National Registries or registries based on personal initiatives of medical associations and scientific organizations. Participants/materials setting methods: In all, 1347 clinics offering ART services in 40 countries reported a total of 918 159 treatment cycles, involving 156 002 with IVF, 407 222 with ICSI, 248 407 with FER, 27 069 with preimplantation genetic testing, 73 927 with egg donation (ED), 654 with IVM of oocytes and 4878 cycles with frozen oocyte replacement (FOR). European data on IUI using husband/partner's semen (IUI-H) and donor semen (IUI-D) were reported from 1197 institutions offering IUI in 29 and 24 countries, respectively. A total of 162 948 treatments with IUI-H and 50 467 treatments with IUI-D were included. A total of 13 689 FP interventions from 11 countries including oocyte, ovarian tissue, semen and testicular tissue banking in pre-and postpubertal patients were reported. Main results and the role of chance: In 20 countries (18 in 2015) with a total population of approximately 325 million inhabitants, in which all ART clinics reported to the registry, a total of 461 401 treatment cycles were performed, corresponding to a mean of 1410 cycles per million inhabitants (range 82-3088 per million inhabitants). In the 40 reporting countries, after IVF the clinical pregnancy rates (PR) per aspiration and per transfer in 2016 were similar to those observed in 2015 (28.0% and 34.8% vs 28.5% and 34.6%, respectively). After ICSI, the corresponding rates were also similar to those achieved in 2015 (25% and 33.2% vs 26.2% and 33.2%). After FER with own embryos, the PR per thawing is still on the rise, from 29.2% in 2015 to 30.9% in 2016. After ED, the PR per fresh embryo transfer was 49.4% (49.6% in 2015) and per FOR 43.6% (43.4% in 2015). In IVF and ICSI together, the trend towards the transfer of fewer embryos continues with the transfer of 1, 2, 3 and ≥4 embryos in 41.5%, 51.9%, 6.2% and 0.4% of all treatments, respectively (corresponding to 37.7%, 53.9%, 7.9% and 0.5% in 2015). This resulted in a proportion of singleton, twin and triplet DRs of 84.8%, 14.9% and 0.3%, respectively (compared to 83.1%, 16.5% and 0.4%, respectively in 2015). Treatments with FER in 2016 resulted in twin and triplet DR of 11.9% and 0.2%, respectively (vs 12.3% and 0.3% in 2015). After IUI, the DRs remained similar at 8.9% after IUI-H (7.8% in 2015) and at 12.4% after IUI-D (12.0% in 2015). Twin and triplet DRs after IUI-H were 8.8% and 0.3%, respectively (in 2015: 8.9% and 0.5%) and 7.7% and 0.4% after IUI-D (in 2015: 7.3% and 0.6%). The majority of FP interventions included the cryopreservation of ejaculated sperm (n = 7877 from 11 countries) and of oocytes (n = 4907 from eight countries). Limitations reasons for caution: As the methods of data collection and levels of completeness of reported data vary among European countries, the results should be interpreted with caution. A number of countries failed to provide adequate data about the number of initiated cycles and deliveries. Wider implications of the findings: The 20th ESHRE report on ART and IUI shows a continuous increase of reported treatment numbers and MAR-derived livebirths in Europe. Being already the largest data collection on MAR in Europe, continuous efforts to stimulate data collection and reporting strive for future quality control of the data, transparency and vigilance in the field of reproductive medicine. Study funding/competing interests: The study has no external funding and all costs were covered by ESHRE. There are no competing interests.
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Research question What were the trends in utilization, outcomes and practices in assisted reproductive technology (ART) in Africa between 2013 and 2017? Design Cycle-based data and retrospective summary data were collected cross-sectionally from voluntarily participating ART centres. Results During the 5-year period, 153, 316 ART procedures were reported from 73 centres in 18 countries. ART utilization remained low in all countries and years. Autologous fresh ART was by far the commonest intervention with little change in the pregnancy rate (PR) per aspiration (34.9% in 2013; 31.7% in 2017) and a consistent preponderance of young women. Oocyte donation represented <10% of reported procedures. Although the transfer of multiple embryos prevailed, elective single embryo transfer (eSET) resulted in a PR of 43.2% per transfer in fresh autologous cycles, which was significantly higher compared to non-elective (oSET) cycles (16.6%) and all dual embryo transfers (DET; 37.3%). Compared to eSET, eDET further increased the PR by less than 5% while raising the multiple delivery rate by 33.4%. The majority of multiples were born preterm. Many pregnancies were, however, lost to follow up compromising the delivery and birth outcome data. Conclusion ART monitoring has been successfully established in Africa though progress must continue. Although data are not yet representative, best evidence indicates low access to ART. Perinatal outcome supports eSET, but other social determinants responsible for multiple embryo transfers are important factors to consider. Efforts must be directed at improving pregnancy follow-up. Registry data are integral to the widening of access to high-quality ART in Africa.
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Twinning is rare among humans, but there is much variability among populations. Several studies show that certain demographic and socioeconomic factors, such as maternal age, mother’s educational level and income, influence twinning rate. There is no background of analytical studies of twins in Uruguay. To the best of our knowledge, this is the first study that has focused on describing and analyzing Uruguayan twinning rates over a period of 17 years (1999–2015). The birth data were collected from the website of Uruguay’s Ministry of Public Health. Economic data were obtained from Uruguay’s Instituto Nacional de Estadísti’s website for the period 2001–2013, since these variables are defined specifically for that period of time. The statistical software R (The R Project for Statistical Computing) was used. The twinning rate varied from 8.51 to 13 in the studied period. Montevideo has the highest median and the smallest variability in comparison with the other departments. In Uruguay (1999–2015), the highest twinning rate (28.94%) was observed in women aged 45 and older. The analysis also showed a relationship between twin birth rates and the mother’s educational level. In three regions of the country (West, Center and East), twin births show a random pattern but in the other two (North and Metropolitan), there is an increasing trend in the number of twins over time. In conclusion, this study recognizes social, economic and demographic factors that influence in the rate of twin births in Uruguay.
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Objective Until now, little was known about the epidemiological characteristics of twins in China due to a lack of reliable national data. In this study, we aimed to analyze temporal trends and perinatal mortality of twins from China. Methods Data on twins between 2007 and 2014 were obtained from the China National Population-Based Birth Defects Surveillance System. Twin and singleton deliveries after at least 28 weeks of gestation were recruited and followed until postnatal day 42. Twinning rates were defined as the number of twin individuals per 1000 births(stillbirths and live births). The Weinberg’s differential method was utilized to estimate the number of monozygotic and dizygotic twins. Results During 2007–2014, the twinning rate increased by 32.3% from 16.4 to 21.7 per 1000 total births with an average of 18.8‰. Among twins, both the perinatal mortality rate (26.1 per 1000 total births) and neonatal death rate (15.7 per 1000 live births) presented a downward tendency but remained at a high level. Large urban-rural and geographic disparities were identified in twinning rates, in perinatal and neonatal mortality, and in their temporal trends. Conclusions The upward trend of twinning rates in China paired with the relatively high rates of perinatal and neonatal mortality among twins highlights the need for improved perinatal care in the light of socio-demographic differences.
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STUDY QUESTION What is the evidence pertaining to availability, effectiveness and safety of ART in sub-Saharan Africa? SUMMARY ANSWER According to overall limited and heterogeneous evidence, availability and utilization of ART are very low, clinical pregnancy rates largely compare to other regions but are accompanied by high multiple pregnancy rates, and in the near absence of data on deliveries and live births the true degree of effectiveness and safety remains to be established. WHAT IS KNOWN ALREADY In most world regions, availability, utilization and outcomes of ART are monitored and reported by national and regional ART registries. In sub-Saharan Africa there is only one national and no regional registry to date, raising the question what other evidence exists documenting the status of ART in this region. STUDY DESIGN, SIZE, DURATION A systematic review was conducted searching Pubmed, Scopus, Africawide, Web Of Science and CINAHL databases from January 2000 to June 2017. A total of 29 studies were included in the review. The extracted data were not suitable for meta-analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS The review was conducted according to Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines. All peer-reviewed manuscripts irrespective of language or study design that presented original data pertaining to availability, effectiveness and safety of ART in sub-Saharan Africa were eligible for inclusion. Selection criteria were specified prior to the search. Two authors independently reviewed studies for possible inclusion and critically appraised selected manuscripts. Data were analysed descriptively, being unsuitable for statistical analysis. MAIN RESULTS AND THE ROLE OF CHANCE The search yielded 810 references of which 29 were included based on the predefined selection and eligibility criteria. Extracted data came from 23 single centre observational studies, two global ART reports, two reviews, one national data registry and one community-based study. ART services were available in 10 countries and delivered by 80 centres in six of these. Data pertaining to number of procedures existed from three countries totalling 4619 fresh non-donor aspirations in 2010. The most prominent barrier to access was cost. Clinical pregnancy rates ranged between 21.2% and 43.9% per embryo transfer but information on deliveries and live births were lacking, seriously limiting evaluation of ART effectiveness. When documented, the rate of multiple pregnancy was high with information on outcomes similarly lacking. LIMITATIONS, REASONS FOR CAUTION The findings in this review are based on limited data from a limited number of countries, and are derived from heterogeneous studies, both in terms of study design and quality, many of which include small sample sizes. Although representing best available evidence, this requires careful interpretation regarding the degree of representativeness of the current status of ART in sub-Saharan Africa. WIDER IMPLICATIONS OF THE FINDINGS The true extent and outcome of ART in sub-Saharan Africa could not be reliably documented as the relevant information was not available. Current efforts are underway to establish a regional ART data registry in order to report and monitor availability, effectiveness and safety of ART thus contributing to evidence-based practice and possible development strategies. STUDY FUNDING/COMPETING INTERESTS No funding was received for this study. The authors had no competing interests. TRIAL REGISTRATION NUMBER PROSPERO CRD42016032336
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Study question Was the European IVF Monitoring (EIM) Consortium, established in 1999 by ESHRE, able to monitor the trend over time of ART in Europe? Summary answer The initial aims of the EIM programme (to collect and publish regional European data on census and trends on ART utilization, effectiveness, safety and quality) have been achieved. What is already known ART data in Europe have been collected and reported annually in Human Reproduction. Study design, size, duration A retrospective data analysis and summary of the first 15 years of ART activity in Europe (1997–2011) was carried out, using the key figures from the annual ESHRE reports and focusing on how the practice of ART has evolved over the years. Participants/materials, setting, method A total of 5 919 320 ART cycles are reported, including IVF, ICSI, frozen embryo relacment and egg donation, resulting in the birth of more than 1 million infants. A total of 1 548 967 IUIs are also reported, including husband/partner’s semen and donor semen cycles. The most relevant and complete data are analysed and discussed. Main results and the role of chance With some fluctuations, the number of countries and clinics reporting to EIM increases significantly from 1997 to 2011. A constant increase was also registered in the number of annual cycles reported. Since 2005, the estimation of the EIM coverage on the total European activity was >80%. In countries with 100% of coverage, the mean availability of ART increased from 765 cycles per million inhabitants in 1997 to 1269 cycles per million inhabitants in 2011, and the proportion of ART infants of the total number of infants born in the country increased from 1.3% to 2.4%. The proportion of women aged > 39 years undergoing IVF and ICSI cycles gradually increased. For 12 consecutive years, the proportion of ICSI versus IVF cycles showed a marked increase before reaching a plateau from 2008. The proportion of transfers with three or more embryos decreased constantly and the proportion of SETs increased over the time period. The triplets deliveries were reduced from 3.7% in 1997 to less than 1% since 2005 (0.6% in 2011). The effectiveness (evaluated as clinical pregnancy rate per aspiration and per embryo transfer) increased until 2007, then the figure remained stable. The cumulative percentage of documented pregnancy losses was 17%. No differences have been noted in terms of outcomes in the IUI cycles. Limitations, reasons for caution The data presented are accumulated from countries with different collection systems, regulations, insurance coverage and different practices. Each year a number of countries have been unable to provide some of the data. Wider implications of the finding(s) The first summary of 15 years of the EIM reports offers interesting data on census and trends on ART utilization, safety and quality in Europe. The primary aim of the ESHRE effort in supporting European data collection has been reached. Owing to its importance inside and outside the professional community, European data collection and publication on ART have to be supported and implemented. Study funding/competing interest(s) None.
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Background: Sub-Saharan Africa has the world's highest under-5 and neonatal mortality rates as well as the highest naturally occurring twin rates. Twin pregnancies carry high risk for children and mothers. Under-5 mortality has declined in sub-Saharan Africa over the last decades. It is unknown whether twins have shared in this reduction. Methods: We pooled data from 90 Demographic and Health Surveys for 30 sub-Saharan Africa countries on births reported between 1995 and 2014. We used information on 1 685 110 singleton and 56 597 twin livebirths to compute trends in mortality rates for singletons and twins. We examined whether the twin–singleton rate ratio can be attributed to biological, socioeconomic, care-related factors, or birth size, and estimated the mortality burden among sub-Saharan African twins. Findings: Under-5 mortality among twins has declined from 327·7 (95% CI 312·0–343·5) per 1000 livebirths in 1995–2001 to 213·0 (196·7–229·2) in 2009–14. This decline of 35·0% was much less steep than the 50·6% reduction among singletons (from 128·6 [95% CI 126·4–130·8] per 1000 livebirths in 1995–2001 to 63·5 [61·6–65·3] in 2009–14). Twins account for an increasing share of under-5 deaths in sub-Saharan Africa: currently 10·7% of under-5 mortality and 15·1% of neonatal mortality. We estimated that about 315 000 twins (uncertainty interval 289 000–343 000) die in sub-Saharan African each year. Excess twin mortality cannot be explained by common risk factors for under-5 mortality, including birthweight. The difference with singletons was especially stark for neonatal mortality (rate ratio 5·0, 95% CI 4·5–5·6). 51·7% of women pregnant with twins reported receiving medical assistance at birth. Interpretation: The fate of twins in sub-Saharan Africa is lagging behind that of singletons. An alarming one-fifth of twins in the region dies before age 5 years, three times the mortality rate among singletons. Twins account for a substantial and growing share of under-5 and neonatal mortality, but they are largely neglected in the literature. Coordinated action is required to improve the situation of this extremely vulnerable group. Funding: None.
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The twinning rate has increased dramatically over the last four decades in developed countries. Two main factors account for this increase: delayed childbearing, as older women tend to have twins more frequently than younger ones, and the expansion of medically assisted reproduction (MAR), which carries an increased probability of multiple births. Using civil registration data, we estimate the share of the increase in twinning rates attributable to the rise in the age at childbearing and to MAR. The effect of MAR is estimated to be about three times as important as the effect of delayed childbearing. Negative health outcomes associated with multiple births and the cost of MAR have raised concerns. We find that in one-quarter of developed countries with the relevant data, the twinning rate reached a plateau around the early 2000s and decreased thereafter. We examine the reasons for this reversal, in particular changes in MAR policies and practices.
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BACKGROUND Infertility is estimated to affect as many as 186 million people worldwide. Although male infertility contributes to more than half of all cases of global childlessness, infertility remains a woman's social burden. Unfortunately, areas of the world with the highest rates of infertility are often those with poor access to assisted reproductive techniques (ARTs). In such settings, women may be abandoned to their childless destinies. However, emerging data suggest that making ART accessible and affordable is an important gender intervention. To that end, this article presents an overview of what we know about global infertility, ART and changing gender relations, posing five key questions: (i) why is infertility an ongoing global reproductive health problem? (ii) What are the gender effects of infertility, and are they changing over time? (iii) What do we know about the globalization of ART to resource-poor settings? (iv) How are new global initiatives attempting to improve access to IVF? (v) Finally, what can be done to overcome infertility, help the infertile and enhance low-cost IVF (LCIVF) activism?
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Objective: To evaluate the outcome for all infants born before 33 weeks gestation until discharge from hospital. Design: A prospective observational population based study. Setting: Nine regions of France in 1997. Patients: All births or late terminations of pregnancy for fetal or maternal reasons between 22 and 32 weeks gestation. Main outcome measure: Life status: stillbirth, live birth, death in delivery room, death in intensive care, decision to limit intensive care, survival to discharge. Results: A total of 722 late terminations, 772 stillbirths, and 2901 live births were recorded. The incidence of very preterm births was 1.3 per 100 live births and stillbirths. The survival rate for births between 22 and 32 weeks was 67% of all births (including stillbirths), 85% of live births, and 89% of infants admitted to neonatal intensive care units. Survival increased with gestational age: 31% of all infants born alive at 24 weeks survived to discharge, 78% at 28 weeks, and 97% at 32 weeks. Survival among live births was lower for small for gestational age infants, multiple births, and boys. Overall, 50% of deaths after birth followed decisions to withhold or withdraw intensive care: 66% of deaths in the delivery room, decreasing with increasing gestational age; 44% of deaths in the neonatal intensive care unit, with little variation with gestational age. Conclusion: Among very preterm babies, chances of survival varies greatly according to the length of gestation. At all gestational ages, a large proportion of deaths are associated with a decision to limit intensive care.