Open Access
Research
Virginie Van Leeuw,1 Charlotte Leroy,1 Yvon Englert,1,2 Wei-Hong Zhang1,2
To cite: Van Leeuw V,
Leroy C, Englert Y, et al.
Effect of maternal origin on
the association between
maternal height and risk of
preterm birth in Belgium: a
retrospective observational
cohort study. BMJ Open
2018;8:e020449. doi:10.1136/
bmjopen-2017-020449
► Prepublication history for
this paper is available online.
To view these files, please visit
the journal online (http://dx.doi.
org/10.1136/bmjopen-2017020449).
Received 3 November 2017
Revised 16 January 2018
Accepted 15 February 2018
1
Perinatal Epidemiology Center
(CEpiP), Non-profit Organisation,
Bruxelles, Belgium
2
Research Laboratory for
Human Reproduction, Faculty
of Medicine, Université Libre
de Bruxelles (ULB), Bruxelles,
Belgium
Correspondence to
Professor Wei-Hong Zhang;
wzhang@ulb.ac.be
AbstrACt
Objectives To investigate the effect of maternal origin on
the association between maternal height and the risk of
preterm birth (PTB).
Design Retrospective observational cohort study.
setting Two of the three Belgian regions, including
Brussels-Capital and Walloon regions.
Participants A total of 245 204 women spontaneously
delivered live singletons between 2009 and 2013.
Maternal nationality at the time of birth included Belgium,
Congo, French, Italy, Morocco, Poland, Romania and Turkey.
Outcomes measures The outcome variable was
spontaneous PTB, defined as childbirth occurring at less
than 37 weeks’ gestation.
results Average height, demographic characteristics and
the spontaneous PTB rate differed according to maternal
origin, defined as maternal nationality at birth. The pattern
of association between maternal height and the risk of
PTB was not uniform by maternal nationality at birth.
The low maternal height category was associated with a
statistically significant increased risk of spontaneous PTB
for Belgian (adjusted OR (aOR) 1.23, 95% CI 1.16 to 1.32),
Italian (aOR 1.48, 95% CI 1.12 to 1.96) and Polish (aOR
1.76, 95% CI 1.11 to 2.78), respectively. However, this
association was not observed for the women from Congo,
France, Morocco, Romania and Turkey.
Conclusions The association between height and the
risk of PTB was modified by maternal nationality, even for
mothers from the same region of the world. For example,
there was a significant inverse association for the Belgians
and Italians but not for French women. Our data suggest
that PTB risk assessment should take into account the
specific height of maternal origin.
IntrODuCtIOn
Preterm birth (PTB), defined as childbirth
occurring at less than 37 completed weeks,
remains the leading cause of perinatal
morbidity and mortality.1 2 An estimated
14.9 million preterm infants were born in
2010, accounting for 11.1% of all live births
worldwide, ranging from approximately 5%
in European countries to 18% in African
countries.2 The main causal factors linked
to PTB include medical conditions in the
strengths and limitations of this study
► This is a retrospective observational cohort study,
including a large number of migrant mothers in
Belgium, which allowed us to construct eight nationality groups comprising a sufficient number of
individuals to perform stratification by maternal nationality at birth.
► This is the first study to analyse the association between maternal height and preterm birth by examining the homogeny of maternal origin.
► No detailed information regarding obstetrical history, maternal smoking, nutritional status or biological
and genetic markers was available.
mother or the fetus, genetic influences, environmental exposure, infertility treatments,
behavioural and socioeconomic factors, and
iatrogenic PTB.3
The association between maternal height
and the risk of PTB has been investigated.4–10
Some studies showed an inverse association
between maternal height and PTB,4 10 but
some studies did not find any significant association.5–9 A recent study demonstrated that
the association between height and the risk
of PTB varied across various ethnic groups in
USA.11
Belgium has long been a country of immigrants and has become a country with one of
the largest foreign-born populations; 44.9%
of deliveries in Belgium in 2013 were to
foreigners living in the country (ie, women not
of Belgian nationality when giving birth).12
These foreign women were mainly economic
migrants (Italian) in the early 20th century
or people affected by family reunification
(Morocco). They also include civil servants
from European institutions or international
institutions in high-income countries, as
well as asylum seekers and undocumented
workers from low-income and middle-income
countries.
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
1
BMJ Open: first published as 10.1136/bmjopen-2017-020449 on 5 April 2018. Downloaded from http://bmjopen.bmj.com/ on June 9, 2020 by guest. Protected by copyright.
Effect of maternal origin on the
association between maternal height
and risk of preterm birth in Belgium: a
retrospective observational cohort study
Open Access
MethODs
study design
This was a retrospective cohort study, using the population-based data linking birth registry and hospital medical
data.
setting
The setting for the study was two of the three regions
in Belgium, including Brussels-Capital and Walloon
regions. Brussels is located in the centre of the country,
and Wallonia is the Southern part of Belgium. The total
annual number of births in the two regions is approximately 62 000 and covers 47 maternity units, and the
majority of deliveries (99.6%) take place in maternity
units.12
Participants
Participants included single live births from 2009 to 2013
in CEpiP’s-linked database who met the inclusion criteria.
The inclusion criteria were as follows: singleton live
births, spontaneous delivery, born at 22–42 weeks of
gestation and women who had nationality at birth from
the eight most represented nationalities in the database, including Belgium, Congo, France, Italy, Morocco,
Poland, Romania and Turkey.
The reason for including only the eight most represented nationalities is based on the estimation of the
sample size in logistic regression analysis to achieve
predictive stability.14 Assuming an average PTB rate of
5% in each model of the eight nationalities, and eight
predictor variables contained in the model, at least 10
events per variable, a total of 80 events (PTB) or at least
1600 subjects (80/5%) were required in each model,
with 80% power and a two-sided significance level of 5%.
Among the eight nationalities meeting the sample size
estimation and included in the analysis, the largest categories were Belgian (n=69 705), Moroccan (n=14 046),
French (n=5020), Italian (n=3922), Turkish (n=3259),
Congolese (n=2924), Romanians (n=2904) and Polish
(n=1924).
Exclusion criteria were as follows: induction of labour
or elective caesarean (defined as a section planned
before the onset of labour), gestational weeks at
delivery <22 or >42, birth weight <500 g, maternal age <18
years, unknown level of education and missing body mass
index (BMI).
Data sources
The study population consisted of all single live births
from 2009 to 2013 in the database of the CEpiP in
Belgium. The database linked the routing data of birth
registry and hospital medical data. The birth registry
legally includes certificates of all live births or stillbirths from 500 g or 22 weeks’ gestation regardless of
maternal citizenship, including asylum seekers, undocumented persons, planned and unplanned home
births. The socioeconomic data were completed by the
civil registration service or by parents when declaring
the birth/death within 15 days of delivery. The hospital
medical data are collected and completed by care
providers in each maternity unit. The details of this
linkage, data management and verification have been
described previously.13 Briefly, CEpiP-linked routing
data contained information regarding maternal
demographics, including maternal origin, maternal
risk factors, medically assisted procedures, delivery
method and perinatal outcomes. Linked data are available for 299 840 live births and 2132 stillbirths during
2009–2013.
Two variables related to the maternal origin were
available in CEpiP’s database: one is the nationality of
the mother at her birth (named ‘maternal nationality at
birth’), and the other is her nationality at delivery (named
‘maternal nationality at delivery’).
Variables
The prepregnancy weight and maternal height were registered at the first prenatal consultation at <12 weeks or
based on self-reports if the first consultation was held >12
weeks. In this paper, the maternal nationality is defined as
the maternal nationality at birth.
To obtain an overview of the distribution of maternal
height among maternal nationalities, we calculated the
25th, 50th and 75th percentile values of maternal height
based on the entire obstetric population (all deliveries).
Furthermore, in order to compare among the included
population, maternal height was classified into three
categories based on height distribution, namely, <25th
(short), 25th–75th (middle) and >75th (tall), specific
for each maternal nationality, with the middle category
serving as reference.
Potential confounding factors for PTB based on previous
study and availability on CEpiP’s database included the
following: maternal age (<25, 25–34 and >35 years),
maternal education based on the highest level achieved
(secondary or less, postsecondary or higher), employment status (yes, no), parity (primipara, multipara),
maternal BMI (<18.5 kg/m2, 18.5–24.9 kg/m2, ≥25.0 kg/
m2), gestational or permanent hypertension (yes, no),
gestational or permanent diabetes (yes, no), medically
assisted conception (yes, no).
2
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
BMJ Open: first published as 10.1136/bmjopen-2017-020449 on 5 April 2018. Downloaded from http://bmjopen.bmj.com/ on June 9, 2020 by guest. Protected by copyright.
The Centre for Perinatal Epidemiology (CEpiP) in
Belgium collects mandatory perinatal official data from
Wallonia and Brussels and covers all the deliveries in
the two regions regardless of citizenship. Information
regarding maternal nationality both at birth and at
delivery is available for each woman in CEpiP’s database.
The aim of this study is to investigate the association
between maternal height and the risk of PTB stratified
by maternal nationality at birth. We use the nationality of
each mother at birth without any categorisation, which
allows us to construct highly homogeneous groups within
the study population.
Open Access
Main outcome and measurement
The outcome variable was spontaneous PTB, defined as
childbirth occurring at less than 37 completed weeks.
The spontaneous birth includes all deliveries after a spontaneous labour.
statistical methods
Baseline characteristics of the study population were
summarised with counts (percentages) for all categorical
variables. Continuous variables were tested with one-way
analysis of variance (ANOVA). Categorical variables
were compared with the X2 test. Occurrence of spontaneous PTB at <37 weeks and its 95% CI was estimated
for each maternal nationality. To determine the relationships between maternal height and risk of spontaneous PTB, crude OR and 95% CI were calculated across
the maternal nationalities. Logistic regression models
were used for controlling eight confounding variables
such as maternal age, maternal education, employment
status, parity, maternal BMI, hypertension, diabetes and
medically assisted conception. Models were stratified by
maternal nationality.
All tests were two tailed and used significance level set
at 0.05. All analyses were performed using Stata V.14.0
software.
ethics approval
Individual information was not available.
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
results
A total of 245 204 women delivered in two regions from
2009 to 2013 and belong to eight groups according to
maternal nationality. Missing data on maternal height
were 10.1% for all deliveries (n=24 763). The 25th, 50th
and 75th percentile values of maternal height of entire
obstetric population (all deliveries) who had available
data on maternal height were calculated (n=220 441)
(figure 1). Calculation based on the overall obstetric
population allowed us to obtain an overview of the distribution of maternal height according to maternal origin
and to avoid selection bias by excluding non-spontaneous
labour for obstetric indications. The average (SD) height
from lowest to the highest was 162 cm (5.7) for Turks
(n=6601), 162 cm (6.3) for Italians (n=9079), 163 cm (5.9)
for Moroccans (n=28 021), 163 cm (6.5) for Romanians
(n=4195), 165 cm (6.3) for French (n=9879), 165 cm
(6.4) for Belgians (n=152 414), 166 cm (5.9) for Polish
(n=3732) and 166 cm (6.5) for Congolese (n=6520).
Through one-way ANOVA, we found that the difference
of mean height between the eight groups was statistically
significant (p<0.001).
For the eight groups of maternal nationality most represented in CEpiP’s database, there were 220 441 pregnancies with height information; 215 767 singleton live births
were identified and linked, and 89 580 subjects were
excluded due to induction of labour or elective caesarean
(41.5% of singleton live births). Births were also excluded
3
BMJ Open: first published as 10.1136/bmjopen-2017-020449 on 5 April 2018. Downloaded from http://bmjopen.bmj.com/ on June 9, 2020 by guest. Protected by copyright.
Figure 1 Box plot of maternal height for the overall obstetric population in eight groups according to maternal nationality at
birth. The bottom (left) and top (right) of the box represent 25th and 75th percentiles, the band in the middle represents the
median (50th percentile). The lower whisker represents the minimum value of the data while the upper whisker represents the
maximum value of the data (analysis of variance, p<0.001).
Open Access
birth without any categorisation of nationality according
to region. Various maternal origins had various height
distributions and various spontaneous PTB rates. Maternal
origin influenced the association between height and the
risk of PTB. These differences also existed for the women
from same world regions or same income group. Belgian,
Italian and French women have been grouped into same
subgroup in previous studies of the effect of maternal
origin on birth outcome.
Maternal short stature as a risk factor for PTB has been
investigated previously with mixed results. A significant
association has been found in a large study reported by
Smith et al,5 in a study that examined teenage pregnancies7 and in a study done by Kramer et al. Some studies
did not demonstrate that maternal height predicted the
risk of PTB, such as in Germany,15 Great Britain,8 Sudan4
and among a homogeneous Chinese population.16 A
significant association was found in a univariable model
or unadjusted data but not for multivariable model or
adjusted data.6 9 10 These mixed results could be partly due
to varying definitions of short stature or height cut-offs,
variation in quality of studies, heterogeneous populations
and small sample sizes in the subgroups.11 17
DIsCussIOn
Main findings
This study examined the association between maternal
height and the risk of spontaneous PTB according to
maternal origin, defined as the maternal nationality at
effect of maternal origin on the association
Our findings are consistent with those of a recent study
conducted in California, which showed that patterns
of association between height and risk of spontaneous
PTB varied according to the maternal ethnicity.11 In the
present study, an inverse significant association between
height and risk of PTB was found for Belgians, Italians
and Polish. However, this association was not observed
for women from Congo, France, Morocco, Romania or
Turkey. Our findings are in line with studies supporting
maternal origin as a modifier in a similar manner. For
example, a study from Canada reported that the association between area characteristics and birth outcomes
was modified by maternal birthplace: area poverty was
associated with PTB among Canadian-born women
but not among foreign-born mothers.18 Another study
from the USA reported that cumulative exposure to
income inequality was associated with PTB for Hispanic
mothers but not for black or white mothers.19 The
causes of birth outcome disparities by maternal origin
are complex and unclear. During recent decades,
disparities in adverse birth outcomes have been documented across subgroups of maternal origin, including
ethnicity, maternal place of birth, maternal nationality
at birth and migrant status.
Some studies reported worse birth outcomes for
foreign-born women compared with native women, with
more obstetrical interventions, perinatal mortality,20 low
birth weight,21 PTB22 and increased caesarean section.23
Some studies showed mixed results.24 25 These inconsistent results could be partly explained by grouping women
with different origins, cultures and maternal characteristics into the same subgroups according to ethnicity classification, geographical regions or income groups.24
4
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
BMJ Open: first published as 10.1136/bmjopen-2017-020449 on 5 April 2018. Downloaded from http://bmjopen.bmj.com/ on June 9, 2020 by guest. Protected by copyright.
if the gestational weeks at delivery were <22 or >42 or
unknown (n=52), birth weight <500 g (n=12), maternal
age <18 years (n=1005), unknown level of education (n=19
002) and missing BMI (n=3240). Therefore, a total of 102
876 births across eight nationalities were included in the
following univariate and logistic regression analyses.
The characteristics of mothers differed according to
maternal nationality for all variables in table 1 (p<0.001).
Concerning the socioeconomic characteristics, mothers
from Belgium, French and Italy were more educated and
more employed than women from Poland, Romania,
Congo, Morocco and Turkey. Regarding medical characteristics, mothers from three non-European countries
(Congo, Morocco and Turkey) were more frequently
multiparous and more overweight. In contrast, these
women had less usage of medically assisted treatment.
The highest proportion of diabetic women was found
in Moroccan women (8.3%), and the lowest proportion of diabetic women was found in Romanian women
(4.1%). For the frequency of hypertension, the highest
was observed for women from Congo (6.4%) and lowest
for women from Morocco (1.7%) and Romania (1.8%).
Figure 2 shows that the PTB rate varied among the
various maternal nationalities. Rates were highest for
women from Italy (7.7%) and Belgium (7.6%) and
lowest for Moroccan women (4.5%). There were similar
trends between PTB rate and the maternal height categories: the lower the maternal height, the higher the
PTB rate, except for Congolese, Romanian and Polish
women, where the PTB rate in the tall group were
slightly higher than that of the middle group (table 2).
The effects of maternal nationality at birth on the
association between height and the risk of PTB are
displayed in table 3. Compared with the middle height
category, the low height category was associated with
a statistically significant increased risk of spontaneous
PTB, with an adjusted OR (aOR) of 1.23 (95% CI 1.16
to 1.32) for Belgians, 1.48 (95% CI 1.12 to 1.96) for
Italians and 1.76 (95% CI 1.11 to 2.78) for Polish. This
relationship was not statistically significant for the
remaining five nationality groups, although a similar
inverse association was observed with or without adjustment for maternal age, education level, employment
status, parity, maternal BMI, hypertension, diabetes and
medically assisted conception.
The direction and strength of the associations between
higher height categories and the risk of PTB was less
pronounced (table 3). After adjustment, the higher height
category was significantly associated with a decreased risk
of spontaneous PTB only for Belgians, with an aOR of
0.82 (95% CI 0.76 to 0.89).
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
Table 1
The characteristics of the population included in the study according to maternal nationality at birth
Belgium N=69 705
Congo N=2904
French N=5020
Italy N=3922
Morocco N=14 046
Poland N=1924
Romania N=2904
530 (10.6)
391 (10.0)
2547 (18.1)
197 (10.2)
646 (30.8)
Turkey N=3259
P values†
Maternal age, year, n (%), n=102 876
<25
11 981 (17.2)
498 (17.2)
819 (25.1)
25–34
47 323 (67.9)
1773 (61.0)
3338 (66.5)
2569 (65.5)
8572 (61.0)
1340 (69.7)
1205 (57.5)
2019 (62.0)
≥35
10 401 (14.9)
633 (21.8)
1152 (22.9)
962 (24.5)
2927 (20.8)
387 (20.1)
245 (11.7)
421 (12.9)
P values†
Reference
***
***
***
***
***
***
Secondary or less
34 196 (49.1)
2126 (73.2)
1967 (39.2)
2160 (55.1)
11 842 (84.3)
1249 (64.9)
1613 (77.0)
2805 (86.1)
Postsecondary or higher
35 509 (50.9)
778 (26.8)
3053 (60.8)
1762 (44.9)
2204 (15.7)
675 (35.1)
483 (23.0)
454 (13.9)
P values†
Reference
***
***
***
***
1316 (68.8)
853 (41.0)
1044 (32.2)
597 (31.2)
1228 (59.0)
2196 (67.8)
***
***
***
***
Education level, n (%), n=102 876
***
***
***
***
Employment status, n (%), n=102 110
Yes
51 195 (74.0)
977 (34.0)
3578 (71.9)
2748 (70.4)
3837 (27.5)
No
17 965 (26.0)
1897 (66.0)
1400 (28.1)
1155 (29.6)
10 124 (72.5)
P values†
Reference
***
***
***
***
***
***
Parity, n (%), n=102 694
1 (primipara)
33 319 (47.9)
865 (29.9)
2410 (48.1)
1967 (50.2)
4757 (33.9)
956 (49.7)
977 (46.6)
1138 (35.0)
≥2 (multipara)
36 238 (52.1)
2032 (70.1)
2603 (51.9)
1950 (49.8)
9278 (66.1)
968 (50.3)
1119 (53.4)
2117 (65.0)
P values†
Reference
***
0.813
0.005
***
0.244
***
0.122
***
BMI, n (%), n=102 876
<18.5 kg/m2
5442 (7.8)
403 (8.0)
250 (6.4)
484 (3.5)
126 (6.6)
166 (7.9)
18.5–24.9 kg/m2
44 677 (64.1)
1453 (50.0)
3462 (69.0)
2498 (63.7)
7544 (53.7)
1426 (74.1)
1412 (67.4)
1931 (59.3)
≥25.0 kg/m2
19 586 (28.1)
1364 (47.0)
1155 (23.0)
1174 (29.9)
6018 (42.8)
372 (19.3)
518 (24.7)
1194 (36.6)
P values†
Reference
***
***
***
***
***
0.003
1729 (96.8)
1980 (98.3)
58 (3.3)
35 (1.7)
87 (3.0)
134 (4.1)
***
***
Medically assisted conception, n (%), n=99 384
No
64 908 (96.0)
Yes
2689 (4.0)
2671 (97.6)
P values‡
Reference
***
No
66 052 (95.3)
2715 (94.7)
Yes
3295 (4.8)
P values†
Reference
0.151
No
67 303 (96.8)
2714 (93.7)
Yes
2251 (3.2)
P values†
Reference
67 (2.4)
4540 (95.9)
3598 (95.0)
13 263 (97.9)
196 (4.1)
191 (5.0)
284 (2.1)
0.585
***
***
0.117
***
1781 (94.7)
1953 (95.9)
99 (5.3)
84 (4.1)
3094 (97.5)
81 (2.5)
***
***
Diabetes, n (%), n=99 384
153 (5.3)
4798 (96.2)
3648 (93.5)
12 734 (91.7)
192 (3.9)
254 (6.5)
1153 (8.3)
0.004
***
***
0.301
0.188
1868 (97.2)
2048 (98.2)
53 (2.8)
38 (1.8)
3036 (93.8)
202 (6.2)
***
***
Hypertension, n (%), n=102 648
***
4900 (97.8)
3810 (97.4)
13 774 (98.3)
108 (2.2)
103 (2.6)
244 (1.7)
***
0.037
***
0.243
***
3184 (98.0)
66 (2.0)
***
***
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5
***P<0.0001.
†χ2 test comparing eight groups of maternal nationality.
‡χ 2 test comparing women who had Belgian nationality at birth.
BMI, body mass index.
Open Access
184 (6.4)
Open Access
For many maternal characteristics, the present data
showed a significantly different pattern among the
selected eight groups of maternal nationality at birth.
These variations persisted among the Belgian, French
and Italian women who are categorised into the same
subgroup of high income according to the definition of
the World Bank Atlas Method (http://data.worldbank.
org/), which is often used in Europe for classification of
immigrant’s country in the previous studies.25 It may be
more appropriate to analyse the association between the
maternal height and the risk of PTB separately according
to their own nationality group, in order to avoid the effect
of heterogeneity within the subgroup.
We show herein that the variation in the rate of PTB
differed according to maternal nationality, the lowest rate
being for Moroccan women. This has also been reported
in a previous study in the Netherlands that demonstrated
a higher risk of PTB for Surinamese and Ghanaian
women compared with Dutch women but a lower risk
for Turkish and Moroccan women.26 A study in the USA
reported that Arab-Americans had a lower risk for PTB
than white Americans.27
Mechanisms between maternal stature, risk of Ptb and role of
maternal origin
A few possible mechanisms have been proposed to
explain the relationship between maternal stature and
risk of PTB. Genetic, transgenerational, early life and
environmental factors may play a role in this relationship.
Pelvic dimensions and shapes vary as well among ethnic
groups.28 A small pelvis was more prevalent in women
with short stature.29 If maternal short stature leads to
shortened gestation by increasing the risk of idiopathic
preterm labour, then short women had more risk of
PTB.30 Short maternal stature was associated with lower
uterine volume and blood flow, increasing the risk for
Table 2 Spontaneous preterm birth (PTB) (<37 weeks) rate by maternal height categories in eight selected groups of maternal
nationality at birth
Overall PTB
Maternal nationality
6
PTB by height categories
Rank
n
%
Short %
Middle %
Tall %
Italian (n=3922)
Belgian (n=69 705)
1
2
301
5321
7.7
7.6
10.3
9.4
7.2
7.4
5.9
6.0
Congolese (n=2904)
3
199
6.9
7.2
6.3
7.7
French (n=5020)
4
326
6.5
7.3
6.8
4.6
Turks (n=3259)
5
205
6.3
7.8
6.2
4.9
Romanians (n=2904)
6
130
6.2
7.0
5.8
5.9
Polish (n=1924)
Moroccans (n=14 040)
7
8
116
626
6.0
4.5
8.6
4.9
4.9
4.3
5.7
4.1
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
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Figure 2 Preterm birth (PTB) rate and 95% CI for eight selected groups of maternal nationality at birth.
Open Access
Maternal height categories
Small
Middle Tall
Crude OR (95% CI) aOR* (95% CI)
OR
Crude OR (95% CI) aOR (95% CI)
Belgian (n=69 705)
Congolese (n=2904)
1.30 (1.23 to 1.39)†
1.15 (0.81 to 1.61)
1.23 (1.16 to 1.32)†
1.12 (0.77 to 1.63)
1
1
0.81 (0.75 to 0.87)†
1.25 (0.87 to 1.79)
0.82 (0.76 to 0.89)†
1.29 (0.87 to 1.91)
French (n=5020)
1.09 (0.84 to 1.41)
1.00 (0.72 to 1.27)
1
0.66 (0.48 to 0.93)†
0.75 (0.53 to 1.06)
Italian (n=3922)
1.47 (1.13 to 1.93)†
1.48 (1.12 to 1.96)†
1
0.81 (0.59 to 1.11)
0.90 (0.65 to 1.25)
Moroccans (n=14 040) 1.14 (0.95 to 1.37)
1.07 (0.89 to 1.30)
1
0.94 (0.76 to 1.17)
0.92 (0.73 to 1.14)
Polish (n=1924)
1.81 (1.19 to 2.75)†
1.76 (1.11 to 2.78)†
1
1.17 (0.70 to 1.96)
1.16 (0.67 to 2.02)
Romanians (n=2904)
Turks (n=3259)
1.23 (0.83 to 1.84)
1.29 (0.93 to 1.78)
1.10 (0.72 to 1.70)
1.35 (0.97 to 1.88)
1
1
1.02 (0.63 to 1.65)
0.78 (0.54 to 1.15)
0.98 (0.59 to 1.62)
0.77 (0.51 to 1.16)
Maternal nationality
*Adjusted for: maternal age, education level, employment status, parity, maternal BMI, hypertension, diabetes and medically assisted
conception.
† P-value <0.001
aOR, adjusted OR; BMI, body mass index.
fetal grow restriction, cephalopelvic disproportion and
caesarean section.29 The effect of ethnicity on gestational
length was also reported in a study in the UK.31 Maternal
short stature may be associated with a lack of nutrients.
Undernourished girls often grow up to become women
of below-average height and often give birth to smaller
infants.30 Shorter women having chronic malnutrition
may be more likely to have infection during pregnancy,
resulting a high risk of PTB.32 Placental epigenetic modification contributes to intrauterine growth and to adulthood height determination.33
limitations and strengths
Several limitations of the present study should be highlighted. First, certain maternal and fetal risk factors for
PTB were not accounted for, including smoking, prior
PTB, nutritional status, infection, acculturation, stress/
depression, family support, uterine contractions, cervical
length and biological/genetic markers. All these factors
may confound or modify the relationship between height
and PTB. Second, our findings should be interpreted
with caution because of a high rate of missing or incomplete information regarding height (10%), educational
level (18%) and BMI (3%), although the proportion of
these missing data did not vary across the eight groups of
maternal nationality. Third, the analysis was limited by the
reporting and coding in the database which was linked
from birth certificates and hospital discharge data. In
particular, weight was self-reported if the first consultation
was held >12 weeks. In addition, diabetes and hypertension
were documented in different forms, either pre-existing or
recognised during pregnancy, regardless of the diagnostic
criteria used. Several techniques and definitions may have
been used across the country, and we cannot exclude that
this could affect our results.
The strength of our study is that it is population based,
with a low rate of missing data and a large set of covariates.
Another strength is the availability of a large number of
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
migrant mothers in Belgium, which has allowed to construct
eight nationality groups including enough individuals to
perform stratification by maternal nationality at birth. This
allowed us to overcome the heterogeneity of misclassification bias of subgroups due to a small number of subjects
in each group. To our knowledge, this is the first study to
analyse the association between maternal height and PTB
according to maternal nationality at birth.
COnClusIOn
The association between height and the risk of PTB is
modified by maternal nationality, even for mothers from
the same region of the world. For example, there was a
significant inverse association for Belgian and Italian,
but not for French women. Our results suggest that PTB
risk assessment should take into account both height and
maternal origin.
Acknowledgements We thank the Brussels Health Observatory and the Health
Department of the French Community of Belgium for their help in gathering the
databases.
Contributors VVL participated in gathering and correcting the data and contributed
to the design of the study and analysing data. CL participated in gathering and
correcting the data and in revising the manuscript. YE participated in the design
of the study and in revising the manuscript. W-HZ participated in the design of
the study and in drafting the manuscript. The final manuscript has been read and
approved by all the authors.
Funding The study was supported by the grant from the Wallonia and Brussels
Health Observatory.
Competing interests None declared.
Patient consent Not required.
ethics approval No ethical approval was required as this study extracted
anonymous data from the CEpiP database.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The dataset supporting the conclusions of this article are
available on request at CepiP perinatalite@cepip.be
Open Access This is an Open Access article distributed in accordance with the
Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which
7
BMJ Open: first published as 10.1136/bmjopen-2017-020449 on 5 April 2018. Downloaded from http://bmjopen.bmj.com/ on June 9, 2020 by guest. Protected by copyright.
Table 3 Maternal height and risk for preterm birth <37 weeks according to the maternal nationality at birth
Open Access
8
Van Leeuw V, et al. BMJ Open 2018;8:e020449. doi:10.1136/bmjopen-2017-020449
© Article author(s) (or their employer(s) unless otherwise stated in the text of the
article) 2018. All rights reserved. No commercial use is permitted unless otherwise
expressly granted.
reFerenCes
BMJ Open: first published as 10.1136/bmjopen-2017-020449 on 5 April 2018. Downloaded from http://bmjopen.bmj.com/ on June 9, 2020 by guest. Protected by copyright.
1. Beck S, Wojdyla D, Say L, et al. The worldwide incidence of preterm
birth: a systematic review of maternal mortality and morbidity. Bull
World Health Organ 2010;88:31–8.
2. Blencowe H, Cousens S, Oestergaard MZ, et al. National, regional,
and worldwide estimates of preterm birth rates in the year 2010 with
time trends since 1990 for selected countries: a systematic analysis
and implications. Lancet 2012;379:2162–72.
3. Goldenberg RL, Culhane JF, Iams JD, et al. Epidemiology and causes
of preterm birth. Lancet 2008;371:75–84.
4. Elshibly EM, Schmalisch G. The effect of maternal anthropometric
characteristics and social factors on gestational age and birth weight
in Sudanese newborn infants. BMC Public Health 2008;8:244.
5. Smith GC, Shah I, White IR, et al. Maternal and biochemical
predictors of spontaneous preterm birth among nulliparous women:
a systematic analysis in relation to the degree of prematurity. Int J
Epidemiol 2006;35:1169–77.
6. Meis PJ, Michielutte R, Peters TJ, et al. Factors associated with
preterm birth in Cardiff, Wales. II. Indicated and spontaneous preterm
birth. Am J Obstet Gynecol 1995;173:597–602.
7. Lao TT, Ho LF. Relationship between preterm delivery and maternal
height in teenage pregnancies. Hum Reprod 2000;15:463–8.
8. Honest H, Bachmann LM, Ngai C, et al. The accuracy of maternal
anthropometry measurements as predictor for spontaneous preterm
birth-a systematic review. Eur J Obstet Gynecol Reprod Biol
2005;119:11–20.
9. Savitz DA, Dole N, Herring AH, et al. Should spontaneous and
medically indicated preterm births be separated for studying
aetiology? Paediatr Perinat Epidemiol 2005;19:97–105.
10. Han Z, Lutsiv O, Mulla S, et al. Maternal height and the risk of
preterm birth and low birth weight: a systematic review and metaanalyses. J Obstet Gynaecol Can 2012;34:721–46.
11. Shachar BZ, Mayo JA, Lee HC, et al. Effects of race/ethnicity and
BMI on the association between height and risk for spontaneous
preterm birth. Am J Obstet Gynecol 2015;213:e701–9.
12. Leeuw V V, Ch L, E Y. Données périnatales en Région bruxelloise Année 2014. Brussels: Centre d’Épidémiologie Périnatale, 2015.
13. Minsart AF, Buekens P, De Spiegelaere M, et al. Missing information
in birth certificates in Brussels after reinforcement of data collection,
and variation according to immigration status. A population-based
study. Arch Public Health 2012;70:25.
14. van der Ploeg T, Austin PC, Steyerberg EW. Modern modelling
techniques are data hungry: a simulation study for predicting
dichotomous endpoints. BMC Med Res Methodol 2014;14:137.
15. Voigt M, Heineck G, Hesse V. The relationship between maternal
characteristics, birth weight and pre-term delivery: evidence
from Germany at the end of the 20th century. Econ Hum Biol
2004;2:265–80.
16. Lao TT, Pun TC. Preterm birth unrelated to maternal height in
Asian women with singleton gestations. J Soc Gynecol Investig
2001;8:291–4.
17. Honest H, Hyde CJ, Khan KS. Prediction of spontaneous preterm
birth: no good test for predicting a spontaneous preterm birth. Curr
Opin Obstet Gynecol 2012;24:422–33.
18. Auger N, Giraud J, Daniel M. The joint influence of area income,
income inequality, and immigrant density on adverse birth outcomes:
a population-based study. BMC Public Health 2009;9:237.
19. Reagan PB, Salsberry PJ. Race and ethnic differences in
determinants of preterm birth in the USA: broadening the social
context. Soc Sci Med 2005;60:2217–28.
20. Reeske A, Kutschmann M, Razum O, et al. Stillbirth differences
according to regions of origin: an analysis of the German perinatal
database, 2004-2007. BMC Pregnancy Childbirth 2011;11:63.
21. Zanconato G, Iacovella C, Parazzini F, et al. Pregnancy outcome
of migrant women delivering in a public institution in northern Italy.
Gynecol Obstet Invest 2011;72:157–62.
22. Cacciani L, Asole S, Polo A, et al. Perinatal outcomes among
immigrant mothers over two periods in a region of central Italy. BMC
Public Health 2011;11:294.
23. Minsart AF, De Spiegelaere M, Englert Y, et al. Classification of
cesarean sections among immigrants in Belgium. Acta Obstet
Gynecol Scand 2013;92:204–9.
24. Urquia ML, Glazier RH, Blondel B, et al. International migration
and adverse birth outcomes: role of ethnicity, region of origin and
destination. J Epidemiol Community Health 2010;64:243–51.
25. Gillet E, Saerens B, Martens G, et al. Fetal and infant health
outcomes among immigrant mothers in Flanders, Belgium. Int J
Gynaecol Obstet 2014;124:128–33.
26. Goedhart G, van Eijsden M, van der Wal MF, et al. Ethnic differences
in preterm birth and its subtypes: the effect of a cumulative risk
profile. BJOG 2008;115:710–9.
27. El-Sayed AM, Galea S. Explaining the low risk of preterm birth
among arab americans in the United States: an analysis of 617451
births. Pediatrics 2009;123:e438–e445.
28. Moloy HC. Evaluation of the pelvis in obstetrics. Philadelphia:
Saunders, 1951.
29. Christian P. Maternal height and risk of child mortality and
undernutrition. JAMA 2010;303:1539–40.
30. Kramer MS, McLean FH, Eason EL, et al. Maternal nutrition and
spontaneous preterm birth. Am J Epidemiol 1992;136:574–83.
31. Patel RR, Steer P, Doyle P, et al. Does gestation vary by ethnic
group? A London-based study of over 122,000 pregnancies with
spontaneous onset of labour. Int J Epidemiol 2004;33:107–13.
32. Schaible UE, Kaufmann SH. Malnutrition and infection: complex
mechanisms and global impacts. PLoS Med 2007;4:e115.
33. Timasheva Y, Putku M, Kivi R, et al. Developmental programming
of growth: genetic variant in GH2 gene encoding placental growth
hormone contributes to adult height determination. Placenta
2013;34:995–1001.
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