Risks of pregnancy and birth in obese primiparous women: An analysis of German perinatal statistics

Abstract

To compare risks of pregnancy and birth in obese (body mass index, BMI ≥ 30) and normal weight women (BMI 18.5-24.99) giving birth to their first child.
We analysed data of 243,571 pregnancies in primiparous women from the German perinatal statistics of 1998-2000. We calculated odds ratios (ORs) with 95% confidence intervals (CIs) for selected pregnancy and birth risks. ORs were adjusted for the confounding factors age, smoking status, single mother status, and maternal education.
Obesity during pregnancy is common in primiparous women (n = 19,130; 7.9% of all cases) and it is significantly associated with a number of risks of pregnancy and birth, including diabetes [OR 3.71 (95% CI 2.93; 4.71); p < 0.001], hypertension [OR 8.44 (7.91; 9.00); p < 0.001], preecalmpsia/eclampsia [OR 6.72 (6.30; 7.17); p < 0.001], intraamniotic infection [OR 2.33 (2.05; 2.64); p < 0.001], birth weight ≥ 4,000 g [OR 2.16 (2.05; 2.28); p < 0.001], and an increased rate of Caesarean section [OR 2.23 (2.15; 2.30); p < 0.001]. Some risks were less frequent in the obese such as cervical incompetence [OR 0.55 (0.48; 0.63); p < 0.001] and preterm labour [OR 0.47 (0.43; 0.51); p < 0.001].
Obesity during pregnancy is an important clinical problem in primiparous women because it is common and it is associated with a number of risks of pregnancy and birth. Because of these increased risks, obese women need special attention clinically during the course of their first pregnancy. Weight reduction before the first pregnancy is generally indicated in obese women to prevent the above-mentioned complications of pregnancy and birth.

Full text

MATERNO-FETAL MEDICINE
Risks of pregnancy and birth in obese primiparous women:
an analysis of German perinatal statistics
Volker Briese •Manfred Voigt •Josef Wisser •
Ulrike Borchardt •Sebastian Straube
Received: 3 April 2009 / Accepted: 24 December 2009 / Published online: 23 January 2010
ÓThe Author(s) 2010. This article is published with open access at Springerlink.com
Abstract
Purpose To compare risks of pregnancy and birth in
obese (body mass index, BMI C30) and normal weight
women (BMI 18.5–24.99) giving birth to their first child.
Methods We analysed data of 243,571 pregnancies in
primiparous women from the German perinatal statistics of
1998–2000. We calculated odds ratios (ORs) with 95%
confidence intervals (CIs) for selected pregnancy and birth
risks. ORs were adjusted for the confounding factors
age, smoking status, single mother status, and maternal
education.
Results Obesity during pregnancy is common in primipa-
rous women (n=19,130; 7.9% of all cases) and it is sig-
nificantly associated with a number of risks of pregnancy and
birth, including diabetes [OR 3.71 (95% CI 2.93; 4.71);
p\0.001], hypertension [OR 8.44 (7.91; 9.00); p\0.001],
preecalmpsia/eclampsia [OR 6.72 (6.30; 7.17); p\
0.001], intraamniotic infection [OR 2.33 (2.05; 2.64);
p\0.001], birth weight C4,000 g [OR 2.16 (2.05; 2.28);
p\0.001], and an increased rate of Caesarean section [OR
2.23 (2.15; 2.30); p\0.001]. Some risks were less frequent
in the obese such as cervical incompetence [OR 0.55 (0.48;
0.63); p\0.001] and preterm labour [OR 0.47 (0.43; 0.51);
p\0.001].
Conclusions Obesity during pregnancy is an important
clinical problem in primiparous women because it is
common and it is associated with a number of risks of
pregnancy and birth. Because of these increased risks,
obese women need special attention clinically during the
course of their first pregnancy. Weight reduction before the
first pregnancy is generally indicated in obese women to
prevent the above-mentioned complications of pregnancy
and birth.
Keywords Body mass index Parity Diabetes 
Hypertension Preeclampsia
Introduction
Obesity is common among women of childbearing age.
Recent estimates of the prevalence of obesity in adults
approach a quarter of the population [1,2]. Some other
work puts the prevalence of obesity in pregnancy at about
10–11% [3,4].
The consequences of obesity in pregnancy include a
number of adverse outcomes for mother and child. A large
retrospective cohort study from UK found that gestational
diabetes, preeclampsia, delivery by emergency Caesarean
section, postpartum haemorrhage, urinary tract infection,
V. Briese
Department of Obstetrics and Gynaecology,
University of Rostock, Rostock, Germany
M. Voigt
Institute for Perinatal Auxology,
Klinikum Su
¨dstadt, Rostock, Germany
J. Wisser (&)
Department of Obstetrics and Gynaecology,
University Hospital Zurich, Frauenklinikstrasse 10,
Zurich 8091, Switzerland
e-mail: josef.wisser@usz.ch
U. Borchardt
Research Institute for the Biology of Farm Animals (FBN),
Research Unit Genetics and Biometry,
Dummerstorf, Germany
S. Straube
Department of Occupational and Social Medicine,
University of Go
¨ttingen, Go
¨ttingen, Germany
123
Arch Gynecol Obstet (2011) 283:249–253
DOI 10.1007/s00404-009-1349-9

wound infection, birth weight above the 90th centile, and
intrauterine death were more common in the obese [3]. An
analysis of German perinatal statistics demonstrated higher
rates of hypertension, preeclampsia, gestational diabetes,
Caesarean section, fetal macrosomia, fetal structural
anomalies, and low neonatal Apgar score for obese com-
pared to normal weight women [4,5]. The adverse health
effects of maternal obesity extend beyond pregnancy. In
women as in men, obesity is a risk factor for the devel-
opment of hypertension, diabetes, and dyslipidaemia.
Maternal obesity also influences offspring outcomes well
beyond the neonatal period. For example, a recent study
observed a correlation between obesity in 9-year-olds and
maternal pregestational weight [6].
Perinatal outcomes are often influenced by parity and for
this reason we wanted to examine the effects of obesity in
pregnancy separately for women who experience their first
pregnancy. In this study, we therefore set out to analyse the
prevalence of pregnancy and birth risks in obese primipa-
rous women compared to primiparous women of normal
weight based on a large set of data from German perinatal
statistics.
Materials and methods
Data for this study were taken from the German perinatal
statistics of 1998–2000. Collection of perinatal statistics
is mandatory in Germany. The German federal states
Bavaria, Brandenburg, Hamburg, Mecklenburg-Western
Pomerania, Lower Saxony, Saxony, Saxony-Anhalt, and
Thuringia contributed data. Our database contains 508,926
datasets from singleton pregnancies in total. Among these
were 243,571 datasets from primiparous women, i.e. data
collected during the first pregnancy. These data formed the
basis of the present analysis.
By convention, obesity was defined by a body mass
index (BMI) C30 and normal weight by a BMI between
18.5 and 24.99. We compared obese primiparae to normal
weight primiparae with regard to the following pregnancy
risks that are coded for in German perinatal statistics: co-
agulopathies, diabetes mellitus (known before pregnancy),
small stature, previous infertility treatment, hypertension,
proteinuria ([1%), moderate to severe edema, gestational
diabetes, cervical incompetence, preterm labour, anaemia,
hypotension. Furthermore, we investigated these birth
risks: premature rupture of membranes, postterm birth, in
utero fetal demise, preterm birth, preeclampsia/eclampsia,
intraamniotic infection, pyrexia during delivery, occur-
rence of an abnormal cardiotocogram (CTG) or concerning
fetal heart sounds, occurrence of green amniotic fluid,
occurrence of fetal acidosis during delivery (as evidenced
by fetal blood sampling), prolonged first stage of labour,
prolonged second stage of labour, cephalopelvic dispro-
portion, transverse presentation, high fetal head station,
birth weight C4,000 g, and the rate of Caesarean sections.
Nominal data are expressed as percent values. For
bivariate analyses the chi-squared test was used. Multi-
variable logistic regression models were used to assess the
association between risks of pregnancy or birth and BMI.
The models were adjusted for age, smoking status, single
mother status, and maternal education. Age was catego-
rised into three groups: B22, 23–31, and C32 years.
Smoking status was categorised into non-smokers, smokers
consuming B10 cigarettes/day, and smokers consuming
C11 cigarettes/day. Regarding maternal education, women
were either ‘‘without qualification’’, i.e. classified as
‘‘unskilled labourers’’ in German perinatal statistics or
were ‘‘others’’ when they were given an occupational
classification other than ‘‘unskilled labourer’’. Odds ratios
(ORs) with 95% confidence intervals (CIs) were calculated.
A value of p\0.05 was considered statistically significant.
All statistical analyse were performed with SPSS software,
version 15.0.
Results
Figure 1shows the distribution of BMI among primiparous
women. Of all cases, 68.4% were of normal weight
(n=166,675) and 7.9% were obese (n=19,130). The
analyses described below are a comparison between these
two groups. Table 1summarises some characteristics of
the two groups that we expected to be confounding factors.
It can be seen that obese and normal weight primiparae
differed significantly with regard to age, smoking status,
single mother status, and maternal education. Because
these parameters can also be expected to influence the
prevalences of the pregnancy and birth risks that form the
focus of this study, it was necessary to adjust for these as
confounding factors in our analyses.
Table 2illustrates some risks of pregnancy coded for
in German perinatal statistics. From the adjusted OR, it is
apparent that obese primiparous women have higher odds
of coagulopathies, diabetes, hypertension, proteinuria, and
edema but lower odds of cervical incompetence, preterm
labour, anaemia, and hypotension. In all cases the dif-
ferences were statistically highly significant (p\0.001).
The highest odds increases associated with obesity could
be observed for hypertension (adjusted OR 8.44), mod-
erate to severe edema (adjusted OR 6.11), gestational
diabetes (adjusted OR 4.55), proteinuria (adjusted OR
4.41), and diabetes known before pregnancy (adjusted OR
3.71).
250 Arch Gynecol Obstet (2011) 283:249–253
123

Table 3compares the prevalences of birth risks between
obese and normal weight primiparae. With the exception of
a prolonged second stage of labour, all investigated birth
risks were significantly more common in the obese; and
except for in utero fetal demise the level of significance
was always high (p\0.001). The odds increases were
highest for preeclampsia/eclampsia (adjusted OR 6.72),
cephalopelvic disproportion (adjusted OR 2.41), and in-
traamniotic infection (adjusted OR 2.33). Neonates with
high birth weight (adjusted OR 2.16) and Caesarean sec-
tions (adjusted OR 2.23) were also more than twice as
likely in obese women. A steep increase in the rate of
Caesarean sections (45.7%) was observed in obese women
older than 32 years (data not shown).
Discussion
The present study demonstrates that obesity during preg-
nancy is common in primiparous women and that it
is associated with a number of risks of pregnancy and
birth, including diabetes, hypertension, preecalmpsia,
16
10
12
14
n = 243,571
= 23.5
s = 4.2
M = 22.7
6
8
BMI
18.50 – 24.99
Normal
weight BMI 30.00: 7.9 %
n = 19,130
Percent
0
2
4
n = 166,6 75
68.4 %
BMI 18.49
4.7 %
BMI
25.00 – 29.99
19.0 %
Body mass index (kg/m²)
14.00 –1
4.99
15.00 – 15.99
16.00 – 16.99
17.00–17.99
18.00 –18.99
19.00 – 19.99
20.00–20.99
21.00 –21.99
22.00–22.99
23.00 – 23.99
24.00–24.99
25.00–25.99
26.00–26.99
27.00–27
.99
28.00 – 28.99
29.00–29.99
30.00–30.99
31.00 – 31.99
32.00–32
.99
33.00 – 33.99
34.00 –34
.99
35.00 –35.99
36.00 –36.99
37.00 –37.99
38.00 – 38.99
39.00–39.99
40.00 – 40.99
41.00–41.99
42.00 –42.99
43.00 – 43.99
44.00 – 44.9 9
45.00–45
.99
x
Fig. 1 Distribution of BMI in the study population
Table 1 Characteristics of the study population
Parameter Normal weight
(BMI 18.50–24.99)
Obesity
(BMI C30.00)
p(chi-
squared
test)
Age (years)
B22 20.5 19.2 \0.001
23–31 61.9 64.0
C32 17.6 16.8
Smoking status
Non-smokers 85.6 81.2 \0.001
Smokers: B10 cig./day 11.4 13.6
Smokers: C11 cig./day 3.0 5.2
Single mother
Yes 18.5 16.7 \0.001
No 81.5 83.3
Education
Without qualification
(classified as ‘‘unskilled
labourer’’)
5.6 8.2 \0.001
Others 94.4 91.8
Table 2 ORs for pregnancy risks in obese compared to normal
weight primiparous women
Pregnancy risks OR (95% CI)
a
Coagulopathies 1.68 (1.45; 1.95)*
Diabetes mellitus 3.71 (2.93; 4.71)*
Small stature 1.71 (1.32; 2.21)*
Previous infertility treatment 1.83 (1.69; 1.99)*
Hypertension 8.44 (7.91; 9.00)*
Proteinuria [1%4.41 (4.00; 4.99)*
Edema 6.11 (5.68; 6.58)*
Gestational diabetes 4.55 (3.94; 5.26)*
Cervical incompetence 0.55 (0.48; 0.63)*
Preterm labour 0.47 (0.43; 0.51)*
Anaemia 0.68 (0.57; 0.80)*
Hypotension 0.25 (0.16; 0.39)*
*p\0.001
a
OR adjusted for the following parameters: age, smoking status,
single mother status, and education
Arch Gynecol Obstet (2011) 283:249–253 251
123

intraamniotic infection, fetal macrosomia, and an increased
rate of Caesarean sections. This work builds on previous
analyses of German perinatal statistics but for the first time
focuses on obese primiparous women and analyses preg-
nancy and birth risks associated with obesity in this group
of patients.
Our results are in agreement with other work on preg-
nancy and birth risks among women who deliver their first
child. A study from UK of 1,858 obese and 14,076 normal
weight women found that preecalmpsia (adjusted OR 3.1),
gestational hypertension (adjusted OR 2.2), emergency
Caesarean section (adjusted OR 2.0), preterm delivery at
less than 33 weeks of gestation (adjusted OR 2.0), and birth
weight[4,000 g (adjusted OR 1.9) were significantly more
common in the obese [7]. A retrospective cohort study
from Scotland demonstrated that the risk of elective pre-
term delivery increased with increasing BMI, while the risk
of spontaneous preterm labour decreased [8]. This is in
agreement with the lower risk of preterm labour found in
obese women in the present study. In several other studies,
rates of Caesarean section were increased in obese women
[9–11]. Women, who are overweight or obese before
pregnancy, have an increased risk of Caesarean section,
particularly if they are also short [12].
The association between maternal obesity and delivery
by Caesarean section is also confirmed after controlling for
possible confounders in other recent retrospective and
prospective analyses that were not restricted to primiparous
women [13,14].
There are some limitations to our study. For our statis-
tical analysis, we used patient self-reporting of smoking
status, single mother status, and maternal education. We
have no way of verifying this information. Regarding
smoking, a description of smoking status according to
pregnancy trimester was not possible with our data. There
is evidence that smoking has different effects at different
times during the pregnancy [15]. The decision when a
certain risk factor or disease was present in a given case
was made by the obstetrician who filled in the data col-
lection form (standard data collection form used in German
perinatal statistics, ‘‘Perinatologischer Basis-Erhebungbo-
gen’’). The terms used in this form to describe pregnancy
and birth risks may possibly be applied differently by
different clinicians. We do not think that this is a signifi-
cant limitation; however, because in most instances, the
terms used in the data collection form are unambiguous.
Despite these limitations and predominantly due to the
large number of cases included and the rigorous statistical
analysis performed, we were able to provide a detailed
description of pregnancy and birth risks in obese compared
to normal weight primiparous women.
In conclusion, obesity during pregnancy is an important
clinical problem in primiparous women because it is
common and it is associated with a number of risks of
pregnancy and birth. Because of these risks obese women
need special attention clinically during the course of their
first pregnancy. It follows that weight reduction before the
first pregnancy is generally indicated in obese women as a
preventive measure.
Conflict of interest statement We declare that we have no conflicts
of interest.
Open Access This article is distributed under the terms of the
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
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