New birthweight charts according to parity and type of delivery for the Spanish population

Abstract

Objective:
Birthweight by gestational age charts enable fetal growth to be evaluated in a specific population. Given that maternal profile and obstetric practice have undergone a remarkable change over the past few decades in Spain, this paper presents new Spanish reference percentile charts stratified by gender, parity and type of delivery. They have been prepared with data from the 2010-2014 period of the Spanish Birth Statistics Bulletin.

Methods:
Reference charts have been prepared using the LMS method, corresponding to 1,428,769 single, live births born to Spanish mothers. Percentile values and mean birth weight are compared among newborns according to gender, parity and type of delivery.

Results:
Newborns to primiparous mothers show significantly lower birthweight than those born to multiparous mothers (p<0.036). Caesarean section was associated with a substantially lower birthweight in preterm births (p<0.048), and with a substantially higher birthweight for full-term deliveries (p<0.030). Prevalence of small for gestational age is significantly higher in newborns born by Caesarean section, both in primiparous (p<0.08) and multiparous mothers (p<0.027) and, conversely, the prevalence of large for gestational age among full-term births is again greater both in primiparous (p<0.035) and in multiparous mothers (p<0.007).

Conclusions:
Results support the consideration of establishing parity and type of delivery-specific birthweight references. These new charts enable a better evaluation of the impact of the demographic, reproductive and obstetric trends currently in Spain on fetal growth.

Full text

Gac
Sanit.
2017;31(2):116–122
Original
New
birthweight
charts
according
to
parity
and
type
of
delivery
for
the
Spanish
population
José
Manuel
Terána,b,∗,
Carlos
Vareaa,b,
Cristina
Bernisa,b,
Barry
Bogina,b,
Antonio
González-Gonzálezc,b
aDepartment
of
Biology,
Faculty
of
Sciences,
Madrid
Autonomous
University,
Madrid,
Spain
bSchool
of
Sport,
Exercise
and
Health
Sciences,
Loughborough
University,
Loughborough,
Leicestershire,
United
Kingdom
cDepartments
of
Obstetrics
and
Gynaecology,
Faculty
of
Medicine,
Madrid
Autonomous
University,
Madrid,
Spain
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
10
June
2016
Accepted
29
September
2016
Available
online
1
February
2017
Keywords:
Fetal
development
Maternal
profile
Caesarean
section
Mean
birthweight
Small
for
gestational
age
Large
for
gestational
age
a
b
s
t
r
a
c
t
Objective:
Birthweight
by
gestational
age
charts
enable
fetal
growth
to
be
evaluated
in
a
specific
pop-
ulation.
Given
that
maternal
profile
and
obstetric
practice
have
undergone
a
remarkable
change
over
the
past
few
decades
in
Spain,
this
paper
presents
new
Spanish
reference
percentile
charts
stratified
by
gender,
parity
and
type
of
delivery.
They
have
been
prepared
with
data
from
the
2010–2014
period
of
the
Spanish
Birth
Statistics
Bulletin.
Methods:
Reference
charts
have
been
prepared
using
the
LMS
method,
corresponding
to
1,428,769
sin-
gle,
live
births
born
to
Spanish
mothers.
Percentile
values
and
mean
birth
weight
are
compared
among
newborns
according
to
gender,
parity
and
type
of
delivery.
Results:
Newborns
to
primiparous
mothers
show
significantly
lower
birthweight
than
those
born
to
mul-
tiparous
mothers
(p
<
0.036).
Caesarean
section
was
associated
with
a
substantially
lower
birthweight
in
preterm
births
(p
<
0.048),
and
with
a
substantially
higher
birthweight
for
full-term
deliveries
(p
<
0.030).
Prevalence
of
small
for
gestational
age
is
significantly
higher
in
newborns
born
by
Caesarean
section,
both
in
primiparous
(p
<
0.08)
and
multiparous
mothers
(p
<
0.027)
and,
conversely,
the
prevalence
of
large
for
gestational
age
among
full-term
births
is
again
greater
both
in
primiparous
(p
<
0.035)
and
in
multiparous
mothers
(p
<
0.007).
Conclusions:
Results
support
the
consideration
of
establishing
parity
and
type
of
delivery-specific
birth-
weight
references.
These
new
charts
enable
a
better
evaluation
of
the
impact
of
the
demographic,
reproductive
and
obstetric
trends
currently
in
Spain
on
fetal
growth.
©
2016
SESPAS.
Published
by
Elsevier
Espa˜
na,
S.L.U.
This
is
an
open
access
article
under
the
CC
BY-NC-ND
license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Nuevas
curvas
de
peso
al
nacer
por
paridad
y
tipo
de
parto
para
la
población
espa˜
nola
Palabras
clave:
Desarrollo
fetal
Perfil
materno
Parto
por
cesárea
Peso
medio
al
nacer
Peque˜
no
para
la
edad
gestacional
Grande
para
la
edad
gestacional
r
e
s
u
m
e
n
Objetivo:
Las
tablas
de
peso
al
nacer
por
edad
gestacional
permiten
evaluar
el
crecimiento
fetal
en
una
población
específica.
Dado
que
el
perfil
materno
y
la
práctica
obstétrica
han
experimentado
un
sustancial
cambio
en
las
últimas
décadas
en
Espa˜
na,
este
trabajo
propone
nuevas
tablas
de
referencia
de
percentiles
estratificadas
por
sexo,
paridad
y
tipo
de
parto,
elaboradas
con
los
datos
del
periodo
2010-2014
del
Boletín
Estadístico
de
Partos.
Métodos:
Las
curvas
de
referencia
han
sido
elaboradas
mediante
el
método
LMS,
correspondientes
a
1.428.769
nacidos
vivos
de
partos
simples
y
madres
espa˜
nolas.
Se
comparan
los
valores
por
percentiles
y
la
media
del
peso
al
nacer,
por
sexo,
paridad
y
tipo
de
parto.
Resultados:
Los
nacidos
de
madres
primíparas
muestran
un
peso
menor
que
los
nacidos
de
multíparas
(p
<
0,036).
Los
nacidos
pretérmino
por
cesárea
tienen
un
peso
menor
que
los
nacidos
pretérmino
por
parto
vaginal
(p
<
0,048),
mientras
que
ocurre
lo
contrario
en
los
nacidos
a
término
(p
<
0,030).
La
preva-
lencia
de
nacidos
peque˜
nos
para
la
edad
gestacional
es
mayor
entre
los
nacidos
por
cesárea
de
madres
tanto
primíparas
(p
<
0,08)
como
multíparas
(p
<
0,027),
y
la
prevalencia
de
nacidos
grandes
para
la
edad
gestacional
es
mayor
entre
los
nacidos
a
término
de
madres
tanto
primíparas
(p
<
0,035)
como
multíparas
(p
<
0,007).
Conclusiones:
Los
resultados
apoyan
establecer
referencias
de
peso
al
nacer
por
paridad
y
tipo
de
parto.
Estas
nuevas
curvas
permiten
una
mejor
evaluación
del
impacto
de
las
actuales
tendencias
demográficas,
reproductivas
y
obstétricas
en
Espa˜
na
sobre
el
crecimiento
fetal.
©
2016
SESPAS.
Publicado
por
Elsevier
Espa˜
na,
S.L.U.
Este
es
un
art´
ıculo
Open
Access
bajo
la
licencia
CC
BY-NC-ND
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
∗Corresponding
author.
E-mail
address:
josemanuel.teran@estudiante.uam.es
(J.M.
Terán).
http://dx.doi.org/10.1016/j.gaceta.2016.09.016
0213-9111/©
2016
SESPAS.
Published
by
Elsevier
Espa˜
na,
S.L.U.
This
is
an
open
access
article
under
the
CC
BY-NC-ND
license
(http://creativecommons.org/licenses/by-nc-
nd/4.0/).
Documento descargado de http://www.gacetasanitaria.org el 01/03/2017. Copia para uso personal, se prohíbe la transmisión de este documento por cualquier medio o formato.

J.M.
Terán
et
al.
/
Gac
Sanit.
2017;31(2):116–122
117
Introduction
Fetal
growth
and
birth
outcome
are
associated
with
perinatal
survival
and
health,
with
the
patterns
of
postnatal
growth,
and
with
differential
risk
for
cognitive,
metabolic
and
cardiovascular
disease
later
in
life.1Birthweight
and
gestational
age
are
the
main
peri-
natal
indicators
that
support
this
relationships
between
fetal
and
postnatal
stages,
as
both
variables
(i.e.
reduced
birthweight
and/or
preterm
births)
have
been
associated
with
epigenetic,
hormonal
and
metabolic
regulation
mechanisms
affecting
health
throughout
life
cycle.2Birthweight
for
gestational
age
charts
allow
assessing
the
prevalence
of
small
for
gestational
age
(SGA)
newborns,
those
born
with
a
birthweight
under
10th
percentile
for
their
gesta-
tional
age.
However,
fetal
growth
charts
prepared
for
one
specific
population
are
not
appropriate
for
evaluating
growth
in
different
populations
as
clinically
important
differences
in
both
the
mean
birthweight
and
percentile
values
may
be
found.3These
differences
are
due
to
biosocial
characteristics
of
the
population
used
as
the
reference
and
the
study
methodology.
Thus,
it
is
important
to
dif-
ferentiate
between
reference
growth
curves
and
standard
growth
curves,
as
Rao
and
Tompkins4remember:
reference
curves
show
the
fetal
growth
of
a
particular
population
at
a
specific
time,
while
standard
curves
show
how
a
newborn
should
grow
according
to
an
ideal
healthy
growth,
and
hence
are
of
prescriptive
nature.
Different
growth
charts
by
gestational
age
and
sex
have
been
designed
for
Spanish
newborns
based
on
hospital
data.5–9 Some
of
these
charts
are
still
widely
used
in
the
Spanish
public
health
system
for
assessing
birth
outcome
and
infant
growth
although
Spain
has
officially
adopted
the
new
WHO
standards
for
term
births
and
up
to
five
years
old
children.10 Most
recently,
Ramos
et
al.11
and
González-González
et
al.12 have
proposed
models
for
calcu-
lating
optimal
fetal
and
neonatal
weight
curves
from
population
and
hospital
data
respectively,
and
García-Mu˜
noz
Rodrigo
et
al.13
have
published
the
first
growth
standards
for
very
preterm
Span-
ish
newborns
(22-28
weeks)
using
data
from
62
hospitals.
Most
of
these
charts
were
prepared
without
differentiating
parity
and
type
of
delivery.
However,
parity
is
a
well-recognized
predictor
of
infant
birthweight,
with
infants
born
to
primiparous
women
registering
significantly
lower
birthweight
and
higher
prevalence
of
intrauter-
ine
growth
restriction
(IUGR).14 At
the
same
time,
the
increasing
rates
of
induced
deliveries
and
Cesarean
sections
(CS)
before
week
37
has
been
associated
with
the
increased
prevalence
of
preterm
births
with
extremely
low
weight
in
developed
countries.15,16
The
profile
of
Spanish
(national)
mothers
has
undergone
a
sig-
nificant
change
over
the
past
decades,
with
a
sustained
increase
in
the
percentage
of
mothers
who
start
reproducing
at
later
ages,
as
well
as
in
the
rates
of
obstetric
interventions
in
general,
and
CS
deliveries
in
particular.17 From
2008
onwards
the
economic
crisis
is
strengthening
these
trends,18 specifically
the
growing
predom-
inance
of
primiparous
mothers
of
ever-increasing
age.
According
to
the
latest
available
data,19 54.3%
of
Spanish
mothers
are
primi-
parous
with
an
average
age
for
first
maternity
of
31.06
years,
while
the
rate
of
CS
is
25.2%
—a
figure
that
is
double
that
recommended
by
WHO20—,
with
higher
rates
in
private
hospitals
and
in
public
hospitals
with
a
lower
technological
level.21 As
proposed
for
other
European
countries,22 these
trends
in
maternal
profile
and
obstetric
practices
might
be
contributing
towards
trends
of
lowering
mean
birthweight
and
increasing
prevalence
of
low
birth
weight
(LBW:
birthweight
under
2,500
grams)
described
in
Spain.17 In
this
con-
text,
to
stablish
and
compare
charts
of
birthweight
by
parity
and
type
of
delivery
may
contribute
both
to
a
fitter
evaluation
of
the
impact
of
these
trends
on
gestational
growth
and
birth
outcome
in
Spain,
and
to
a
greater
understanding
of
the
causes
underlying
the
sustained
increase
in
the
rate
of
CS
in
the
country.
With
these
aims,
using
data
from
the
Spanish
Birth
Statistics
Bulletin
for
the
period
2010-2014,
the
aim
of
this
study
is
to
prepare
new
reference
charts
of
birthweight
by
gestational
age
in
Spain,
stratified
by
sex,
parity
and
type
of
delivery.
Methods
Data
and
final
sample
The
percentile
tables
and
charts
presented
in
this
study
have
been
prepared
with
cross-sectional
data
from
the
period
2010-
2014
of
the
Spanish
Birth
Statistics
Bulletin
(BEP,
Boletín
Estadístico
de
Partos),
the
compulsory
civil
registration
of
all
births
whatever
the
nationality
or
legal
status
of
residence
of
the
parents
provided
annually
by
the
Spanish
National
Institute
of
Statistics
as
micro-
data
files.
The
process
of
data
collection
and
its
implications
both
for
the
quality
and
interpretation
of
the
epidemiological
results
derived
from
this
source
have
been
evaluated
by
Juárez,23,24 and
Río
et
al.25 Validation
studies
have
concluded
that
data
provided
by
the
Spanish
Birth
Statistics
Bulletin
are
quite
reliable
(␬
=
0.74
for
gestational
age,
and
␬
=
0.88
for
birthweight)
when
compared
with
hospital
birth
data,
although
misreporting
was
significantly
higher
among
immigrants.23 Besides
this
problem,
newborns
from
immigrant
mothers
(n
=
419,161,
18.9%
of
all
live
births)
have
been
excluded
due
to
their
relevant
contribution
to
national
natality
as
well
as
to
the
notorious
differences
in
origin,
lifestyles,
reproduc-
tive
behaviour
and
birth
outcome
among
the
main
groups
of
foreign
mothers
in
Spain.26 Therefore,
percentile
tables
and
charts
pro-
posed
should
apply
only
to
Spanish
mothers.
4.1%
(n
=
71,435)
of
the
Spanish
mothers
were
originally
immigrants
that
obtained
the
Spanish
citizenship,
and
2.9%
(n
=
50,098)
have
a
foreign
husband
or
steady
partner.
Figure
1
shows
the
process
of
selection
of
final
sample.
First,
among
newborns
from
Spanish
mothers,
stillbirths
(n
=
419,161,
18.8%)
were
excluded.
Among
live
births,
newborns
without
data
on
gestational
age
and
birthweight
(n
=
295,882,
13.3%
of
all
live
births)
were
also
eliminated,
as
well
as
those
born
at
gestational
ages
before
24
and
after
42
weeks
(n
=
858,
0.0%),
and
from
multi-
ples
pregnancies
(n
=
35,781,
1.6%).
Finally,
implausible
data
were
also
eliminated
with
outlier
limits
set
at
±1.5
standard
deviation
(SD).
Final
sample
includes
1,428,769
live
births
from
singleton
deliveries
of
Spanish
mothers
(74.4%,
n
=
1,062,319
by
vaginal
deliv-
ery,
and
25.6%,
n
=
366,450
by
CS
delivery),
corresponding
to
64.2%
(n
=
2,224,844)
of
the
total
live
births
born
in
Spain
in
2010-2014,
and
to
79.8%
(n
=
1,789,372)
of
those
from
Spanish
mothers.
Final
sample
does
not
differ
from
the
excluded
data
in
maternal
pro-
file
(age
at
birth,
and
educational
level
and
occupation),
although
the
rate
of
primiparity
is
slightly
higher
(54.9%
compared
to
52.5%,
respectively;
p
<
0.001)
and
the
rate
of
CS
deliveries
slightly
lower
(25.6%
and
26.5,
respectively;
p
<
0.001).
Statistical
analysis
Percentile
tables
and
curves
by
sex,
parity
(primiparous
or
mul-
tiparous
mothers)
and
type
of
delivery
(vaginal
or
by
CS
delivery)
were
prepared
according
to
the
LMS
method.27 The
LMS
method
provides
three
curves
for
each
percentile
chart.
The
first
is
curve
L
(␭),
which
results
from
non-linear
transforming
of
birthweight,
so
this
variable
follows
a
normal
distribution.
The
second
curve,
M
(␮),
corresponds
to
the
median
(percentile
50)
or
average
as
the
distri-
bution
of
the
variable
of
interest
now
has
a
Gaussian
distribution
due
to
adjustment
for
curve
L.
The
last
curve,
S
(␴),
corresponds
to
the
coefficient
of
variation.
To
obtain
parameters
␭,
␮
and
␴,
L,
M
and
S
curves
were
adjusted
by
polynomic
regression
thus
the
curves
obtained
are
those
which
best
represent
an
adjustment
of
these
parameters
that
allow
a
graphic
representation
of
percentile
charts
Documento descargado de http://www.gacetasanitaria.org el 01/03/2017. Copia para uso personal, se prohíbe la transmisión de este documento por cualquier medio o formato.

118
J.M.
Terán
et
al.
/
Gac
Sanit.
2017;31(2):116–122
Initial sample of live
births
Selected only live births
from spanish mothers
Selected only live
births with data for
gestational age and
birthweight
Included sample
N=2,224,844
N=1,789,372
Included sample
Selected gestational age
≥24 and ≤42
N=1,789,372
Included sample
Selected only singleton
Eliminated outliers
N=1,492,632
Included sample
N=1,456,851
Final sample
N=1,428,769
Excluded sample
N=28,082(1.26%)
Excluded sample
N=35,781(1.61%)
Excluded sample
N=858(0.04%)
Excluded sample
N=295,882
(13.30%)
Excluded sample
N=419,161
(18.84%)
Figure
1.
Diagram
of
inclusion/exclusion
process.
(Data
from
Spanish
Birth
Statis-
tics
Bulletin,
single
live
births,
Spanish
mothers,
2010-2014).
and
the
calculation
of
exact
z-scores
(Z)
for
any
value.
Formula
1
allows
calculating
the
values
for
each
percentile:
C
=
M(1
+
LSZ)(1/L);
L
/=
0
(1)
being
C
the
birthweight
of
a
percentile,
L,
M
and
S
are
the
value
of
these
parameters
given
in
Tables
I-VIII
of
the
online
Appendix
of
this
article
for
a
specific
gestational
age,
and
Z
the
corresponding
z-score
for
this
percentile.
Birthweight
charts
and
curves
corresponding
to
3rd,
10th,
50th,
90th
and
97th
percentiles
according
to
parity,
type
of
deliv-
ery
and
sex
of
the
newborn
are
shown
in
Tables
I-VIII
and
Figures
I-VIII
of
the
online
Appendix
of
this
article.
From
the
SD
val-
ues
of
the
mean
included
in
the
tables,
STATA
software
v.12
allows
assessing
the
differences
in
mean
birthweight
(50th
percentile
val-
ues)
by
gestational
age
for
both
sexes
according
to
parity
and
type
of
delivery.
The
SD
of
mean
birthweight
for
each
gestational
age
was
calculated
using
formula
2:
SD
=
MS
(2)
Besides,
formula
3
allows
obtaining
the
z-score
of
a
birthweight
referred
to
a
reference
curve
in
order
to
assess
the
prevalence
of
SGA
and
Large
for
Gestational
Age
(LGA)
by
parity
and
type
of
delivery:
Z
=
[(X/M)L−
1]/(LS);
L
/=
0
(3)
being
X
the
weight
in
grams.
For
each
sex,
the
reference
curve
chosen
is
that
established
for
newborns
delivered
vaginally
and
to
primiparous
mothers
(Tables
I
and
III
of
the
online
Appendix
of
this
article).
Results
Shown
in
Table
1
are
the
number
of
total
births
(N)
and
preva-
lence
of
CS
delivery
by
gestational
age,
sex
of
the
newborn,
and
parity.
The
highest
rates
of
CS
deliveries
occurred
between
weeks
28
and
32,
and
then
again
after
week
40,
both
in
primiparous
and
multiparous
mothers.
The
total
rate
of
CS
deliveries
was
signifi-
cantly
higher
for
primiparous
than
for
multiparous
mothers
(28.8%
and
21.8%
respectively;
␹2=
8,896.015;
d.f.
=
1;
p
<
0.001,
both
sexes
considered).
The
rate
of
CS
was
significantly
higher
among
primiparous
mothers
both
in
preterm
births
(males:
␹2=
53.211,
d.f.
=
1,
p
<
0.001;
and
females:
␹2=
29.557;
d.f.
=
1;
p
<
0.001)
and
in
term
births
(males:
␹2=
5,492.929;
d.f.
=
1;
p
<
0.001;
and
females:
␹2=
3,495.540,
d.f.
=
1,
p
<
0.001).
Tables
I-VIII
(and
Figures
I-VIII)
of
the
online
Appendix
of
this
article
present
the
percentile
values
and
L,
M
and
S
parameters
proposed
for
evaluating
birthweight
by
gestational
age,
sex,
par-
ity
and
type
of
delivery
in
newborns
of
Spanish
mothers.
Based
on
these
data,
Figures
2
and
3
present
the
birthweight
charts
(10th,
50th
and
90th
percentiles)
for
newborns
to
primiparous
and
multi-
parous
women
according
to
sex
and
type
of
delivery.
Independently
of
sex
and
type
of
delivery,
the
mean
birthweight
(50th
percentile)
of
newborns
to
primiparous
mothers
was
significantly
lower
than
that
of
newborns
to
multiparous
mothers
(from
gestational
age
30
weeks
in
males
and
34
weeks
in
females
born
by
vaginal
deliveries,
respectively,
and
from
25
and
26
weeks,
respec-
tively,
in
those
born
by
CS
deliveries:
p
<
0.036;
Tables
IX-
XII
of
the
online
Appendix).
Likewise,
Figures
4
and
5
show
the
birthweight
charts
of
new-
borns
delivered
vaginally
and
by
Cesarean
section
according
to
parity
and
sex.
Independently
of
sex
and
parity,
mean
birthweight
of
preterm
newborns
delivered
by
CS
was
significantly
lower
than
those
delivered
vaginally
(from
24
to
37
weeks
in
males,
and
from
25
to
37
weeks
in
females
to
primiparous
mothers;
and
from
27
to
36
weeks
in
males,
and
from
26
to
36
weeks
in
females
born
to
multiparous
women:
p
<
0.048;
Tables
XIII-XVI
of
the
online
Appendix).
Accordingly,
the
prevalence
of
SGA
was
also
significantly
higher
among
newborns
born
at
early
gestational
ages
by
CS
delivery
compared
with
those
delivered
vaginally,
both
in
primiparous
(from
26
to
38
weeks
of
gestation
in
both
sexes:
p
<
0.08;
Tables
XVII
and
XIX
of
the
online
Appendix)
as
well
as
in
multiparous
mothers
(from
28
to
37
weeks
of
gestation
in
both
sexes:
p
<
0.027;
Tables
XXI
and
XXIII
of
the
online
Appendix).
Con-
versely,
Figures
4
and
5
also
show
that
mean
birthweight
of
term
newborns
delivery
by
Cesarean
section
was
greater
than
those
born
vaginally
(from
38
to
42
weeks
in
both
sexes
and
parities:
p
values
<0.030;
Tables
XIII-XVI
of
the
online
Appendix).
As
expected,
in
these
gestational
ages
prevalence
of
LGA
was
higher
in
newborns
born
by
CS
delivery,
again
both
among
primiparous
(from
36
to
42
weeks
in
males,
and
from
37
to
42
weeks
in
females:
p
<
0.035;
Tables
XVIII-XX
of
the
online
Appendix)
and
multiparous
mothers
(from
37
to
42
weeks
in
males,
and
from
38
to
42
weeks
in
females:
p
<
0.007;
Tables
XXII-XXIV
of
the
online
Appendix).
Documento descargado de http://www.gacetasanitaria.org el 01/03/2017. Copia para uso personal, se prohíbe la transmisión de este documento por cualquier medio o formato.

J.M.
Terán
et
al.
/
Gac
Sanit.
2017;31(2):116–122
119
Table
1
Number
of
total
births
and
prevalence
of
Cesarean
section
deliveries
in
the
study
population
(data
from
Spanish
Birth
Statistics
Bulletin,
single
live
births,
Spanish
mothers,
2010-2014).
Gestational
age
Male
Female
Primiparous
Multiparous
Primiparous
Multiparous
n
CS
(%)
n
CS
(%)
n
CS
(%)
n
CS
(%)
24
81
22.2
65
41.5
69
24.6
36
30.6
25
145
37.2 79
57.0 128
50.8
81
44.4
26
214
51.4
104
53.8
175
58.9
100
54.0
27
256
57.8
117
59.8
201
66.2
127
63.8
28
311
65.3
209
67.0
238
70.2
141
63.8
29
413
65.4
217
66.4
320
69.4
151
64.9
30
536
63.8
325
62.2
386
70.5
225
70.7
31
636
57.5 428
60.7 529
66.2 333
58.9
32
1,127 57.9 786
55.1 815
63.4
551
61.3
33
1,508
50.3
915
46.7
1,093
53.4
686
52.8
34
3,501
42.6
2,318
40.3
2,573
43.8
1,907
43.2
35
5,264
37.0
3,960
34.4
4,131
37.8
3,029
36.8
36
10,395
34.1
8,586
30.5
8,542
35.3
7,096
32.9
37
24,299
32.7
24,503
28.7
21,088
33.7
21,396
29.7
38
58,305
33.3
60,055
30.5
51,949
33.6
54,436
31.1
39
97,579
27.0
88,801
20.7
92,454
25.2
84,321
19.7
40
112,315
25.3
88,927
15.8
111,247
21.5
88,097
13.8
41
76,322
32.8
46,441
18.9
74,059
27.7
44,754
16.6
42
10,829 42.7 5,605
24.2
9,718
35.5
5,110
20.8
Total
of
births
404,036
30.1
332,441
22.5
379,715
27.4
312,577
21.2
n:
number
of
total
births;
CS:
Cesarean
section.
Discussion
This
paper
presents
the
first
nationally
representative
refer-
ence
tables
and
charts
for
birthweight
by
gestational
age
and
sex
according
to
parity
and
type
of
delivery
for
Spanish
population.
These
tables
allow
calculating
the
exact
percentile
or
z-score
of
the
newborn
depending
on
parity,
type
of
birth
and
newborn
sex
due
to
the
inclusion
of
L,
M
and
S
values.
Our
results
support
the
suggestion
by
Hinkle
et
al.28 of
establishing
parity-specific
birth-
weight
references.
Live
births
of
both
sexes
and
all
gestational
ages
born
to
primiparous
mothers
showed
significantly
lower
birth-
weight
than
those
of
multiparous
mothers,
as
Liu
et
al.29 have
recently
confirmed
for
Chinese
population.
Primiparity
determines
a
reduction
in
birthweight
and
is
a
well-known
risk
factor
for
greater
incidence
of
LBW
and
IUGR,
when
other
maternal
char-
acteristics
are
controlled,
including
type
of
delivery.30 The
main
biological
mechanism
proposed
as
an
explanation
of
the
effect
of
parity
on
fetal
growth
is
a
lesser
vascular
uteroplacental
capac-
ity
in
primiparous
mothers,
which
reduces
the
supply
of
oxygen
and
nutrients
to
the
fetus.31,32 There
are
also
structural
factors
for
primiparous
mothers
(such
as
a
less
intra-uterine
space
in
the
first
pregnancy
than
in
later
pregnancies)
which
also
tend
to
reduce
birthweight.33
Results
also
confirm
that
newborns
delivered
by
CS
showed
more
variation
of
weight
at
birth,
depending
on
gestational
age,
than
those
born
vaginally,
as
previous
research
has
shown.34,35
CS
deliveries
were
associated
with
a
substantial,
significant
reduc-
tion
in
birthweight
among
earlier
gestational
ages
of
both
sexes
and
24 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 41 42
Gestational age (weeks)
Primiparous mothers Multiparous mothers
4500
4000
3500
3000
2500
2000
1500
1000
500
024 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 41 42
Gestational age (weeks)
Birthweight (grams)
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Birthweight (grams)
ab
Figure
2.
Birthweight
by
gestational
age
10th,
50th
and
90th
percentiles
for
males
(a)
and
females
(b)
by
vaginal
delivery
to
primiparous
(solid
lines)
and
multiparous
mothers
(dotted
lines).
(Data
from
Spanish
Birth
Statistics
Bulletin,
single
live
births,
Spanish
mothers,
2010-2014).
Documento descargado de http://www.gacetasanitaria.org el 01/03/2017. Copia para uso personal, se prohíbe la transmisión de este documento por cualquier medio o formato.

120
J.M.
Terán
et
al.
/
Gac
Sanit.
2017;31(2):116–122
24 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 41 42
Gestational age (weeks)
Primiparous mothers Multiparous mothers
4500
4000
3500
3000
2500
2000
1500
1000
500
024 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 41 42
Gestational age (weeks)
Birthweight (grams)
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Birthweight (grams)
ab
Figure
3.
Birthweight
by
gestational
age
10th,
50th
and
90th
percentiles
for
males
(a)
and
females
(b)
by
Cesarean
section
delivery
to
primiparous
(solid
lines)
and
multiparous
mothers
(dotted
lines).
(Data
from
Spanish
Birth
Statistics
Bulletin,
single
live
births,
Spanish
mothers,
2010-2014).
all
maternal
parities
in
such
a
way
that
the
distribution
of
the
10th
percentile
is
skewed
towards
lower
birthweight
among
preterm
live
births
delivered
by
CS
compared
with
those
born
vaginally.
As
extreme
low
birthweight
among
preterm
births
is
associated
with
increased
risk
of
neonatal
death,36 the
rising
rates
of
CS
deliveries
at
early
gestational
ages
in
developed
countries
have
been
associated
with
improved
perinatal
survival,15,37 a
positive
trend
supported
by
the
dramatic
technological
breakthroughs
in
Perinatology
and
Neonatology
of
last
decades.
However,
this
obstetric
trend
does
not
explain
the
dramatic
increase
in
CS
deliveries
in
Spain,
given
that
the
most
of
this
type
of
delivery
took
place
among
gestations
of
37
weeks
or
more
—over
90%,
in
both
primiparous
and
multiparous
mothers
(as
can
be
confirmed
from
Table
1).
Certainly,
the
preva-
lence
of
LGA
newborns
was
higher
in
newborns
born
by
CS
delivery
compared
with
those
born
vaginally,
both
among
primiparous
and
multiparous
mothers,
although
not
as
heavily
as
the
previously
described
increase
in
the
prevalence
of
SGA
among
preterm
live
births,
as
figures
4
and
5
clearly
show;
likewise,
although
the
mean
birth
weight
is
significantly
higher
among
term
newborns
born
by
CS
delivery
compared
with
those
born
vaginally,
the
dif-
ferences
are
very
small
(Tables
I-VIII
of
the
online
Appendix).
In
summary,
the
high
rates
of
CS
deliveries
registered
in
Spain
cannot
be
explained
by
a
high
prevalence
of
dystocia
by
macrosomia
or
cephalopelvic
disproportion,
neither
for
primiparous
nor
for
mul-
tiparous
mothers.
As
Bernis
et
al.17 and
Redondo
et
al.21 consider,
research
on
non-clinical
factors
affecting
delivery
could
clarify
the
ever-growing
rate
of
CS
in
Spain,
an
issue
that
goes
beyond
the
objectives
of
this
paper.
Meanwhile,
the
utilization
of
neonatal
charts
for
birthweight
taking
into
account
type
of
delivery
is
highly
recommended
to
evaluate
the
effect
that
the
increase
in
the
rate
of
CS
deliveries
during
the
last
two
decades
in
Spain
would
have
on
the
assessment
of
fetal
growth
if
type
of
delivery
is
not
considered,
24 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 41 42
Gestational age (weeks)
Vaginal delivery Cesarean section delivery
4500
4000
3500
3000
2500
2000
1500
1000
500
024 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 41 42
Gestational age (weeks)
Birthweight (grams)
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Birthweight (grams)
ab
Figure
4.
Birthweight
by
gestational
age
10th,
50th
and
90th
percentiles
for
males
(a)
and
females
(b)
to
primiparous
mothers
by
vaginal
delivery
(solid
lines)
and
Cesarean
section
delivery
(dotted
lines).
(Data
from
Spanish
Birth
Statistics
Bulletin,
single
live
births,
Spanish
mothers,
2010-2014).
Documento descargado de http://www.gacetasanitaria.org el 01/03/2017. Copia para uso personal, se prohíbe la transmisión de este documento por cualquier medio o formato.

J.M.
Terán
et
al.
/
Gac
Sanit.
2017;31(2):116–122
121
24 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 4241
Gestational age (weeks)
24 25 26 27 28 29 30 31 32 33 34 35 34 37 38 39 40 4241
Gestational age (weeks)
Vaginal delivery Cesarean section delivery
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Birthweight (grams)
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Birthweight (grams)
ab
Figure
5.
Birthweight
by
gestational
age
10th,
50th
and
90th
percentiles
for
males
(a)
and
females
(b)
to
multiparous
mothers
by
vaginal
delivery
(solid
lines)
and
Cesarean
section
delivery
(dotted
lines).
(Data
from
Spanish
Birth
Statistics
Bulletin,
single
live
births,
Spanish
mothers,
2010-2014).
particularly
in
order
to
avoid
both
underestimating
the
prevalence
of
SGA
in
preterm
births
and
overestimating
the
prevalence
of
LGA
in
term
births
among
those
delivered
vaginally.38,39
Limitations
of
the
study
The
percentile
tables
presented
here
are
based
on
cross-
sectional
data
from
the
Spanish
Birth
Statistics
Bulletin.
Neverthe-
less,
the
use
of
these
percentile
tables
and
charts
are
restricted
to
newborns
from
Spanish
mothers,
as
those
born
from
foreign
moth-
ers
were
excluded.
Additionally,
some
critical
considerations
can
be
formulate
on
the
origin
and
quality
of
the
data.
Gestational
age
is
calculated
on
the
last
menstrual
period
(LMP)
in
completed
weeks.
Our
findings
may
stand
in
contrast
with
those
based
on
longitudinal
or
cross-sectional
ultrasound
measurements
recorded
during
ges-
tation,
which
improve
the
accuracy
of
gestational
age
assignment
and
allow
calculating
an
estimated
fetal
weight
(EFW).
Compared
with
early
ultrasound
scanning
estimation
of
gestational
age,
LMP
date
more
often
overestimates
the
true
length
of
gestation,
under-
estimating
the
prevalence
of
preterm
birth
and,
consequently,
increasing
the
rate
of
newborns
incorrectly
diagnosed
as
growth
retarded.40 However,
EFW
charts
do
not
avoid
misclassification
of
gestational
age,
which
results
in
the
opposite
effect
of
lowering
birthweight
percentiles
among
preterm
births
and
increasing
the
percentile
values
late
in
gestation.41 Besides
these
methodologi-
cal
considerations,
it
is
necessary
to
remember
that
the
pattern
of
intrauterine
growth
for
term
births
does
not
necessarily
have
to
be
the
same
as
for
preterm
births,
as
spontaneous
preterm
birth
has
been
significantly
associated
with
IUGR.42 Despite
these
limitations
and
differences
between
methods,
the
reference
tables
and
charts
for
birthweight
by
gestational
age
at
birth
are
easier
and
cheaper
to
establish,
allowing
evaluate
temporal
trends
in
fetal
growth
and
weight
at
birth
(including
the
prevalence
of
SGA
and
LGA)
asso-
ciated
with
changes
in
maternal
age,
parity,
and
type
of
delivery,
factors
which
have
registered
notable
changes
in
Spain
over
the
last
decades,
as
well
as
in
other
developed
countries.
Conclusion
The
evaluation
of
fetal
growth
and
its
secular
trends
are
impor-
tant
for
human
biologists,
epidemiologists,
gynaecologists
and
public
health
professionals,
as
birth
weight
is
related
with
peri-
natal
survival
and
health,
with
the
patterns
of
postnatal
growth,
and
with
differential
risk
for
metabolic
and
cardiovascular
disease
later
in
life.
Because
the
main
environmental
factors
involved
in
its
variability
(maternal
profile
and
protocols
of
delivery)
have
been
rapidly
changing
during
the
last
decades
in
Spain
as
in
other
devel-
oped
countries,
there
is
an
increasing
agreement
that
the
temporal
tendencies
of
fetal
growth
and
birth
outcome
must
be
based
on
reference
tables
and
charts
for
birthweight
by
gestational
age
and
sex
according
to
parity
and
type
of
delivery.
Results
support
this
consideration,
giving
important
clues
to
address
the
causes
of
the
increasing
rate
of
CS
deliveries
in
Spain.
What
is
known
about
the
subject?
Parity
and
type
of
delivery
are
associated
with
birthweight
and
have
to
be
considered
when
analysing
birth
outcome.
Maternal
profile
and
obstetric
practices
has
undergone
a
sig-
nificant
change
over
the
past
decades
in
Spain
affecting
birth
outcome,
as
described
in
other
developed
countries.
What
does
this
study
add
to
the
literature?
Based
on
population
data,
new
charts
of
birthweight
by
gestational
age,
sex,
parity
and
type
of
delivery
for
the
Span-
ish
population
are
proposed.
Results
support
the
necessity
of
establishing
parity
and
type
of
delivery-specific
birthweight
references
to
evaluate
birth
outcome
both
at
clinical
and
temporal-population
levels.
Editor
in
charge
Glòria
Pérez.
Transparency
declaration
The
corresponding
author
on
behalf
of
the
other
authors
guar-
antee
the
accuracy,
transparency
and
honesty
of
the
data
and
information
contained
in
the
study,
that
no
relevant
information
has
been
omitted
and
that
all
discrepancies
between
authors
have
been
adequately
resolved
and
described.
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122
J.M.
Terán
et
al.
/
Gac
Sanit.
2017;31(2):116–122
Authorship
contributions
J.M.
Terán
and
C.
Varea
designed
the
study
and
proposed
a
first
draft.
J.M.
Terán
managed
and
analysed
data.
C.
Bernis,
B.
Bogin
and
A.
González-González
contributed
reviewing
the
literature,
editing
all
versions
of
the
paper
and
providing
relevant
contributions.
All
authors
approved
the
final
version.
Funding
The
authors
acknowledge
financial
financial
support
from
the
School
of
Sport,
Exercise
&
Health
Sciences,
Loughborough
Univer-
sity
(UK),
to
help
defray
the
publication
charges
for
this
article.
Conflicts
of
interests
None.
Acknowledgments
Authors
are
very
grateful
to
Dr.
Tanis
R.
Fenton
(Department
of
Community
Health
Sciences,
Faculty
of
Medicine,
University
of
Calgary,
Canada)
for
providing
constructive
comments
on
an
earlier
version
of
the
manuscript.
Appendix.
Supplementary
data
Supplementary
data
associated
with
this
article
can
be
found,
in
the
online
version,
at
doi:10.1016/j.gaceta.2016.09.016.
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