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RESEARCH ARTICLE
Pre-Pregnancy BMI, Gestational Weight Gain,
and the Risk of Hypertensive Disorders of
Pregnancy: A Cohort Study in Wuhan, China
Aifen Zhou
1☯
, Chao Xiong
1,4☯
, Ronghua Hu
1
, Yiming Zhang
1
, Bryan A. Bassig
2
,
Elizabeth Triche
3
, Shaoping Yang
1
, Lin Qiu
1
, Yaqi Zhang
1
, Cong Yao
1
, Shunqing Xu
4
,
Youjie Wang
4
, Wei Xia
4
, Zhengmin Qian
5
, Tongzhang Zheng
2
*, Bin Zhang
1
*
1 Wuhan Women and Children Health Care Center, Wuhan, Hubei, People’s Republic of China,
2 Department of Environmental Health Sciences, Yale School of Public Health, New Haven, CT, United
States of America, 3 Department of Epidemiology, Brown University School of Public Health, Providence, RI,
United States of America, 4 Key Laboratory of Environment and Health, School of Public Health, Tongji
Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of
China, 5 Department of Epidemiology, College for Public Health and Social Justice, Saint Louis University,
MO, United States of America
☯ These authors contributed equally to this work.
* mchwhzb@163.com (BZ); tongzhang.zheng@yale.edu (TZ)
Abstract
Background
Hypertensive disorders of pregnancy (HDP) are major causes of maternal death worldwide
and the risk factors are not fully understood. Few studies have investigated the risk factors
for HDP among Chinese women. A cohort study involving 84,656 women was conducted to
investigate pre-pregnancy BMI, total gestational weight gain (GWG ), and GWG during early
pregnancy as risk factors for HDP among Chinese women.
Methods
The study was conducted between 2011–2013 in Wuhan, China, utilizing data from the
Maternal and Children Healthcare Information Tracking System of Wuhan. A total of 84,656
women with a live singleton pregnancy were included. Multiple unconditional logistic regres-
sion was conducted to evaluate associations between putative risk factors and HDP.
Results
Women who were overweight or obese before pregnancy had an elevated risk of develop-
ing HDP (overweight: OR = 2.66, 95% CI = 2.32–3.05; obese: OR = 5. 53, 95% CI = 4.28–
7.13) compared to their normal weight counterparts. Women with total GWG above the Insti-
tute of Medicine (IOM) recommendation had an adjusted OR of 1.72 (95% CI = 1.54– 1.93)
for HDP compared to women who had GWG within the IOM recommendation. Women with
gestational BMI gain >10 kg/m
2
during preg nancy had an adjusted OR of 3.35 (95% CI =
2.89–3.89) for HDP, compared to women with a gestational BMI gain <5 kg/m
2
. The
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 1/10
OPEN ACCESS
Citation: Zhou A, Xiong C, Hu R, Zhang Y, Bassig
BA, Triche E, et al. (2015) Pre-Pregnancy BMI,
Gestational Weight Gain, and the Risk of
Hypertensive Disorders of Pregnancy: A Cohort
Study in Wuhan, China. PLoS ONE 10(8): e0136291.
doi:10.1371/journal.pone.0136291
Editor: Cheryl S. Rosenfeld, University of Missouri,
UNITED STATES
Received: March 17, 2015
Accepted: August 2, 2015
Published: August 25, 2015
Copyright: © 2015 Zhou et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Data are available from the Wuhan Women and
Children Health Care Center for researchers who
meet the criteria for access to confidential data.
Funding: This work was supported by the Fogarty
training grants D43TW 008323 and D43TW 007864-
01 from the US National Institutes of Health (http://
www.nih.gov/), and Dr. Tongzhang Zheng received
the funding. The funders had no role in study design,
data collection and analysis, decision to publish, or
preparation of the manuscript.
increased risk of HDP was also observed among women with higher early pregnancy (up to
18 weeks of pregnancy) GWG (>600g/wk: adjusted OR = 1.48, 95% CI = 1.19–1.84).
Conclusion
The results from this study show that maternal pre-pregnancy BMI, early GWG, and total
GWG are positively associated with the risk of HDP. Weight control efforts before and dur-
ing pregnancy may help to reduce the risk of HDP.
Introduction
Hypertensive disorders of pregnancy (HDP), consisting of gestational hypertension (GH) and
preeclampsia (PE), are major causes of maternal and perinatal morbidity and mortality [1]. It has
been reported that HDP complicates 5–10% of all pregnancies worldwide and causes up to 70,000
maternal deaths each year [2]. In addition to maternal complications, HDP is also associated with
fetal intrauterine growth restriction and preterm birth [3]. However, effective treatments for HDP
are still limited, and currently the etiology of HDP is not completely understood [4].
Previous studies in developed countries have linked pre-pregnancy obesity to the develop-
ment of HDP suggesting that the risk factors for this condition may not be limited to exposures
during the gestational period [5, 6]. On the other hand, there is increasing concern about
whether gestational weight gain (GWG) may influence the development of HDP and to what
extent control of GWG can reduce the risk of HDP. Several studies have indicated that HDP is
more likely to develop in women with greater GWG [7–9]. However, the majority of previous
studies have only evaluated total GWG during pregnancy in relation to risk of HDP; given that
women with HDP are likely to experience edema during pregnancy [10], which may result in
greater GWG, it is hard to distinguish the weight gain caused by edema from the weight gain
independent of this condition [11]. Therefore, whether GWG is causally related to the develop-
ment of HDP is still unclear. To our knowledge, there has been only one study, which was con-
ducted in the United Kingdom, that addressed this issue by assessing weight gain during early
pregnancy that was likely not the result of edema. Some positive associations between greater
GWG in early pregnancy and increased risk of developing gestational hypertension and pre-
eclampsia were observed in that study [11].
Although the impact of HDP is thought to be much more severe in developing countries than
in developed countries [12], there are limited epidemiological studies that have evaluated risk
factors for HDP among women in developing countries, including in China. As Asian women
generally have a lower BMI prior to pregnancy compared to women in Western countries [13],
the relationship between pre-pregnancy BMI, GWG, and risk of HDP among Asian women may
differ, although these hypotheses have not been extensively studied. Therefore, we conducted a
cohort study to evaluate the association of pre-pregnancy BMI, total GWG, and early pregnancy
GWG with risk of HDP among a relatively large population of women from Wuhan, China.
Methods
Study Population
This is a cohort study conducted in Wuhan, China, utilizing data from the Maternal and Chil-
dren Healthcare Information Tracking System of Wuhan. The tracking system includes infor-
mation pertaining to demographic characteristics, medical history, prenatal examinations,
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 2/10
Competing Interests: The authors have declared
that no competing interests exist.
deliveries, and postnatal visits for mothers and infants from all of the 93 hospitals and 121
community health centers in Wuhan. Enrolled women in our study included those without a
history of chronic hypertension or cardiovascular disease prior to pregnancy, who lived in the
urban area of Wuhan during pregnancy, and who delivered a live singleton newborn with no
birth defects and gestational age no less than 28 weeks between June 1, 2011 and June 10, 2013.
A total of 97,582 women were enrolled initially. We then excluded those with any missing
values for height, pre-pregnancy weight, or GWG. To eliminate extreme outliers, data analysis
was also limited to women whose height, weight, and GWG were within 5 standard deviations
of the mean. A total of 84,656 women met these criteria and were included in the analysis;
63,603 of them had a record of at least one weight measurement during early pregnancy (8–18
weeks). Informed consent was not obtained because data from this study were abstracted from
the healthcare information system without individual identification, and the research protocol
was approved by the Institutional Review Board of Wuhan Women and Children Health Care
Center, in accordance to the principles of the Declaration of Helsinki. All patient records were
anonymized and de-identified prior to analysis.
Exposure Information
Weight measurements during pregnancy were taken routinely as part of antenatal care at the
clinic. Pre-pregnancy weight and height were self-reported at the first antenatal care visit (usu-
ally in the first trimester). Pre-pregnancy BMI was calculated as weight (in kg)/height (in
meters) squared and categorized into four groups based on recommendations by the Working
Group On Obesity in China of the Chinese Ministry of Health: underweight (<18.5 kg/m
2
),
normal weight (18.5–23.9 kg/m
2
), overweight (24–27.9 kg/m
2
), and obese (28 kg/m
2
)[14].
Total GWG was calculated by subtracting pre-pregnancy weight from the weight on deliv-
ery day. GWG was categorized according to the recommendations of the Institute of Medicine
(IOM) (2009) [15]. GWG within the IOM recommendations was defined as 12.5–18 kg, 11.5–
16 kg, 7–11.5 kg, and 5–9 kg respectively for underweight, normal weight, overweight, and
obese women.
Weight measurements between 8–18 weeks gestation were used to evaluate GWG during
early pregnancy. GWG during early pregnancy was evaluated as the average GWG per week up
to 18 weeks of pregnancy, and classified as class I (<200 g/week), class II (200–400 g/week),
class III (400–600 g/week), and class IV (> 600 g/week) [11].
Gestational BMI gain was categorized as minimal (<5 kg/m
2
), moderate (5–10 kg/m
2
), and
excessive (> 10 kg/m
2
) based on evidence from a previous study [7]. Each one point increase
in BMI is roughly equivalent to 2.5 kg in weight gain, using the Chinese nat ional average for
female height at reproductive age (158 cm, 54 kg) [14].
Outcome Assessment
Gestational hypertension and preeclampsia were defined according to the International Society
for the Study of Hypertension [16]. Gestational hypertension was defined as having a maternal
systolic blood pressure (SBP) > 140 mm Hg and/or diastolic blood pressure (DBP) > 90
mmHg, measured on 2 occasions separated by at least 6 hours beginning after 20 weeks gesta-
tion. Preeclampsia was defined using the same criteria in conjunction with proteinuria > 300mg
on a 24-hour urine collection or proteinuria of at least 1+ on dipstick testing [16].
Statistical Analysis
Unconditional logistic regression was conducted to calculate odds ratios (ORs) and 95% confi-
dence intervals (CIs) evaluating the association of each factor (pre-pregnancy BMI, total
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 3/10
pregnancy GWG, GWG in early pregnancy, and gestational BMI gain) and risk of HDP overall,
as well as risk of gestational hypertension and preeclampsia separately. Models were adjusted
for other previously identified risk factors for HDP including maternal age at delivery, educa-
tion level, parity, offspring sex, and gestational week. Separate models were run to evaluate the
associations with HDP for total GWG, GWG during early pregnancy, and gestational BMI
gain, and all of these models were also adjusted for pre-pregnancy BMI. Additionally, models
evaluating the risk of HDP for pre-pregnancy BMI and gestational BMI gain were mutually
adjusted. Analyses were further stratified by maternal pre-pregnancy BMI categories, and the
interactions between GWG and pre-pregnancy BMI were assessed using a Wald test by includ-
ing the relevant cross-product terms in the regression models. Linear trends were tested using
the Wald test. Statistical analyses were conducted using SAS, version 9.3, (SAS Institute, Inc.,
Cary, North Carolina) and P < 0.05 was considered statistically significant.
Results
Table 1 shows selected characteristics of women in the cohort. 1,973 out of 84,656 (2.33%)
women were diagnosed with HDP (including 1,244 cases of GH and 729 cases of PE). Women
aged over 30 years, nulliparous women, and women who were overweight/ obese before preg-
nancy were more likely to develop HDP. The mean total GWG among women who developed
HDP was 19.52±8.21 kg, higher than that of normotensive women (17.44±7.00 kg). The aver-
age GWG up to 18 weeks was also higher among women with HDP (0.219±0.209kg/wk) com-
pared with normotensive women (0.201±0.188kg/wk).
Table 2 presents the associations of pre-pregnancy BMI, gestational BMI gain, total GWG,
and GWG during early pregnancy in relation to risk of HDP . In the model adjusted for con-
founders, pre-pregnancy BMI, gestational BMI gain, and GWG were all positively associated
with the risk of HDP. Women who were obese prior to pregnancy were about 5 times more
likely to develop HDP, compared with women who had a normal pre-pregnancy BMI (adjusted
OR = 5.53, 95% CI = 4.28–7.13). A significantly increased risk of HDP was also observed for
women with a BMI gain greater than 10 kg/m
2
during pregnancy (adjusted OR = 3.35, 95%
CI = 2.89–3.89). Furthermore, women with GWG above the IOM recommendation had an
adjusted OR of 1.72 (95% CI = 1.54–1.93) for developing HDP compared with women who
had GWG within the recommendation.
An increasing risk of HDP was also observed as GWG increased during early pregnancy (p
trend < 0.01). Compared with women who gained less than 200 grams per week before 18
weeks of pregnancy, the risk of developing HDP was significantly higher among women who
gained greater than 400 grams per week (OR = 1.26, 95% CI = 1.07–1.50). Notably, women
who gained greater than 600 grams per week during early pregnancy had the highest risk of
HDP with an adjusted OR of 1.48 (CI = 1.19–1.84).
Results for gestational BMI gain, total GWG, and GWG during early pregnancy stratified by
pre-pregnancy BMI are presented in Table 3. Women with higher BMI gain and GWG during
the whole pregnancy had a significantly elevated risk of developing HDP across all pre-preg-
nancy BMI categories. However, the odds ratio for higher BMI gain and GWG decreased as the
pre-pregnancy BMI increased. In particular, women who were underweight before pregnancy
and who had higher gestational BMI gain (10 kg/m
2
) had the highest risk of developing HDP
(adjusted OR = 3.46, CI = 2.07–5.78), whereas the corresponding ORs were still elevated but
not as strong in women with higher BMI gain who were overweight or obese before pregnancy
(P for heterogeneity < 0.01).
A different trend was apparent fo r the association of early pregnancy GWG and HDP
stratified by pre-pregna ncy BMI ( Table 3). No significantly increased risk of HDP was
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 4/10
observed among women who were underweight before pr egnancy and who had the highest
GWG during early pregnancy (highest level vs lowest level : adjusted OR = 1.34, 95%
CI = 0.71–2.55). Among women with a pre-pregnancy B MI ca tegory classified a s norma l or
overweight/obese, the highest level of GW G (600g/week) during early pregnancy signifi-
cantly elevated the risk of developing HDP, compared to the lowest level of early GWG
(among normal weight women: adjusted OR = 1.42, 95% CI = 1.09–1.85; among overweight/
obese women: adjusted OR = 1.79, 95% CI = 1.09–2.94). There was, however, no significant
heterogeneity between pre-pregnancy BMI categories for the association of GWG during
early pregnancy and HDP risk (P for heterogeneity = 0.71).
Additionally, we assessed the associations of pre-pregnancy BMI, gestational BMI gain,
total GWG, and GWG during early pregnancy with risk of gestational hypertension and pre-
eclampsia separately. These two outcomes were positively associated with all of the evaluated
exposures and the magnitudes of the associat ions were similar (S1 and S2 Tables).
Table 1. Distribution of selected characteristics of the cohort stratified by HDP status.
Maternal characteristic Normotensive
(n = 82,683)
HDP(n = 1,973)
n/mean %/SD n/mean %/SD
Age at delivery
<25 15664 18.94 237 12.01
25–29 42705 51.65 926 46.93
30–34 19009 22.99 556 28.18
35 5305 6.42 254 12.87
Education Level
Less than high school 9515 11.51 222 11.25
High school 37264 45.07 856 43.39
College 31801 38.46 795 40.29
Advanced Degree 4103 4.96 100 5.07
Parity
Nulliparous 68775 83.18 1687 85.50
Multiparous 13908 16.82 286 14.50
Offspring Sex
Male 44097 53.33 1024 51.90
Female 38586 46.67 949 48.10
Gestational week
<37 3030 3.66 266 13.48
37–41 78612 95.08 1691 85.71
42 1041 1.26 16 0.81
Pre-pregnancy BMI(kg/m
2
)
Under weight (<18.5) 14146 17.11 208 10.54
Normal (18.5–23.9) 63271 76.52 1419 71.92
Overweight (24–27.9) 4648 5.62 273 13.84
Obese(28) 618 0.75 73 3.70
Total GWG(Kg) 17.44 7.00 19.52 8.21
Average GWG up to 18 weeks (Kg/wk)* 0.201 0.188 0.219 0.209
*Includes 63,603 subjects with at least one weight measurement during the early pregnancy period
doi:10.1371/journal.pone.0136291.t001
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 5/10
Discussion
During the past decades, HDP remains a leading cause of maternal death worldwide [12]. Pre-
vious studies conducted in developed countries have indicated that obesity and excessive
weight gain during pregnancy pose a significant risk for developing HDP [11, 17, 18]. However,
there have been limited epidemiological studies about risk factors for HDP among Chinese
women.
In this large cohort study conducted among Chinese women, we found that maternal over-
weight /obesity before pregnancy was independently associated with an increased risk of HDP,
compared with women with lower pre-pregnan cy BMI, which is consistent with previous stud-
ies [ 7, 19, 20]. It has been postulated that maternal–fetal immune maladaptation is involved in
the pathogenesis of preeclampsia [1, 21, 22]. Adipose tissue is known to be associated with met-
abolic syndrome including adiposity and hyperlipidemia, which can cause inflammatory
changes and then lead to an increase in oxidative stress. This may result in endothelial dysfunc-
tion, maternal organ hypo perfusion, and eventually clinical diseases such as HDP [23, 24].
Previous studies have also suggested that adipose tissue may stimulate angiogenesis, which has
been recently implicated to be involved in the development of hypertension [25].
Although several previous studies have reported a positive association between excessive
GWG and the risk of HDP, the association has not been confirmed due to the generally limited
number of studies and the potential limitations of previous study designs [26]. The majority of
studies only evaluated the absolute GWG over the entire pregnancy with the risk of HDP and
did not distinguish the weight gain driven by edema and the weight gain caused by adiposity.
Table 2. Associations of pre-pregnancy BMI, gestational BMI gain, total GWG, and GWG during early pregnancy with risk of HDP
a
.
Exposure Variables Normotensive(n) HDP(n) Crude OR(95% CI) Adjusted OR(95% CI)*
Pre-pregnancy BMI(kg/m
2
)
b
Under weight (<18.5) 14146 208 0.66(0.57–0.76) 0.64(0.55–0.74)
Normal (18.5–23.9) 63271 1419 1.00 (ref) 1.00 (ref)
Overweight (24–27.9) 4648 273 2.62(2.29–2.99) 2.66(2.32–3.05)
Obese(28) 618 73 5.27(4.11–6.75) 5.53(4.28–7.13)
Gestational BMI gain (kg/m
2
)
b
<5 20345 384 1.00 (ref) 1.00 (ref)
5–10 53423 1195 1.19(1.06–1.33) 1.46(1.29–1.64)
10 8915 394 2.34(2.03–2.70) 3.35(2.89–3.89)
Total GWG By IOM Recommendation
b
Below 14012 220 0.88(0.75–1.04) 0.88(0.75–1.04)
Within 24927 443 1.00 (ref) 1.00 (ref)
Above 43744 1310 1.69(1.51–1.88) 1.72(1.54–1.93)
Average GWG up to 18weeks(g/wk)
c
<200 37851 803 1.00 (ref) 1.00 (ref)
200–399 15181 342 1.06(0.93–1.21) 1.07(0.94–1.22)
400–599 6199 170 1.29(1.09–1.53) 1.26(1.07–1.50)
600 2963 94 1.50(1.20–1.86) 1.48(1.19–1.84)
P for trend <0.01
a
. Gestational BMI gain, total GWG, and GWG during early pregnancy were evaluated in separate models.
b
. Adjusted for age at delivery, education level, parity, offspring sex, and gestational week. Additionally, pre-pregnancy BMI and gestational BMI gain were
mutually adjusted. Total GWG also adjusted for pre-pregnancy BMI. (n = 84,656)
c
. Adjusted for age at delivery, education level, parity, offspring sex, and pre-pregnancy BMI. (n = 63,603)
doi:10.1371/journal.pone.0136291.t002
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
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As edema is one of the hallmarks of preeclampsia, the etiologic association of GWG and pre-
eclampsia is uncertain in those studies [7, 27], as weight gain during pregnancy may be the
result of edema caused by preeclampsia. To our knowledge, there has been only one study to
date, which was conducted in the United Kingdom [11], that attempted to account for the
weight caused by edema by assessing weight gain during early pregnancy. That study found a
positive association between GWG in early pregnancy and risk of HDP. However, there have
been no such studies among Asian women. In the present study, we found that excessive GWG
during the whole pregnancy was significantly associated with an increased risk of HDP after
adjusting for gestational weeks, which is consistent with previous studies [7, 11]. As BMI is
considered by some to be a better measure of adiposity than weight alone [7], we also classified
antenatal weight gain according to the net change in BMI, and similarly, excessive BMI gain
during pregnancy was shown to be related to an elevated risk of HDP. We additionally evalu-
ated the association of early pregnancy GWG and risk of HDP, and the data indicated that
weight gain before 18 weeks gestation was also positively associated with the risk of HDP. This
association is unlikely to be explained by edema because edema is unlikely to happen at this
stage of pregnancy, which demonstrates that GWG may precede the development of HDP.
Table 3. Associations of gestational BMI gain, total GWG, and GWG during early pregnancy with risk of HDP stratified by pre-pregnancy BMI
a
.
Exposure Variables under-weight (<18.5 kg/m
2
) Normal (18.5–23.9 kg/m
2
) Overweight/Obese(24 kg/
m
2
)
P for
heterogeneity
Crude OR
(95% CI)
Adjusted OR
(95% CI)
Crude OR
(95% CI)
Adjusted OR
(95% CI)
Crude OR
(95% CI)
Adjusted OR
(95% CI)
Gestational BMI gain (kg/
m
2
)
b
<5 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) <0.01
5–10 1.19(0.75–
1.87)
1.35(0.85–2.14) 1.35(1.17–
1.56)
1.45(1.25–1.67) 1.41(1.11–
1.79)
1.47(1.16–1.87)
10 2.80(1.69–
4.62)
3.46(2.07–5.78) 2.94(2.49–
3.48)
3.40(2.87–4.04) 2.12(1.3–
3.45)
2.27(1.39–3.73)
Total GWG By IOM
Recommendation
b
Below 1.31(0.77–
2.23)
1.20(0.70–2.05) 0.82(0.68–
0.99)
0.83(0.69–1.00) 0.77(0.46–
1.28)
0.86(0.52–1.45) 0.35
Within 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref)
Above 2.34(1.69–
3.23)
2.72(1.95–3.79) 1.46(1.29–
1.66)
1.65(1.45–1.87) 1.45(1.08–
1.95)
1.57(1.16–2.11)
Average GWG up to
18weeks(g/wk)
c
<200 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 1.00 (ref) 0.71
200–399 0.95(0.63–
1.44)
0.94(0.62–1.43) 1.06(0.92–
1.24)
1.04(0.90–1.21) 1.27(0.93–
1.73)
1.28(0.94–1.74)
400–599 1.41(0.88–
2.28)
1.40(0.87–2.25) 1.25(1.02–
1.53)
1.21(0.99–1.49) 1.35(0.92–
1.98)
1.34(0.91–1.97)
600 1.38(0.73–
2.62)
1.34(0.71–2.55) 1.48(1.14–
1.93)
1.42(1.09–1.85) 1.75(1.07–
2.86)
1.79(1.09–2.94)
P for trend 0.19 <0.01 <0.01
a
. Gestational BMI gain, total GWG, and GWG during early pregnancy were evaluated in separate models.
b
. Adjusted for age at delivery, education level, parity, offspring sex, and gestational week. (n = 84,656)
c
. Adjusted for age at delivery, education level, parity, and offspring sex. (n = 63,603)
doi:10.1371/journal.pone.0136291.t003
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 7/10
It was found in some studies that an increased risk of preeclampsia and gestational hyper-
tension was present in all women with excessive GWG, except those who were underweight
prior to pregnancy [9], while others found a positive association across all BMI categories [28].
In order to explore whether the pre-pregnancy BMI may modify the association between preg-
nancy weight gain and HDP risk, we stratified the asso ciation by maternal pre-pregnancy BMI
categories, and found a significant association between excessive GWG during the whole preg-
nancy and an elevated risk of HDP across all the pre-pregnancy BMI categories. Our results
also suggested that although the risk of HDP increased with excessive GWG, the risk decreased
as pre-pregnancy BMI increased. A similar trend was observed in the stratified results from
previous studies [29, 30]. However, the results for early pregnancy GWG with HDP stratified
by pre-pregnancy BMI showed a different trend in that the association between early preg-
nancy GWG and HDP was only significant among women who were normal weight and over-
weight/obese before pregnancy. The risk of HDP was not significantly increased among
women who were underweight and who had higher GWG during early pregnancy, and was
highest among women who were overweight/obese before pregnancy and who had the highest
level of early GWG. The different trends observed between whole pregnancy GWG and early
pregnancy GWG when stratified by pre-pregnancy BMI might be explained by the different
levels of edema at the middle or late stage of pregnancy across different pre-pregnancy BMI
categories, which needs to be examined by further prospective studies. Excessive weight gain
during early pregnancy, which may result from changes in diet and physical activity levels
including among women with normal pre-pregnancy BMIs, may lead to an increased risk of
HDP through mechanisms involving oxidative stress [7].
Additionally, we evaluated the risk of gestational hypertension and preeclampsia separately,
and also observed a positive association with pre-pregnancy BMI category, whole pregnancy
GWG, BMI gain, and early pregnancy GWG for both outcomes. The association of excessive
GWG during the whole pregnancy and gestational hypertension alone was consistent with a
large scale cohort study conducted in the United States [7]. As gestational hypertension is by
definition not characterized by proteinuria, women with gestational hypertension would be
expected to have less edema; thus, the impact of weight gain should be more likely to be driven
by adiposity rather than edema in the process of disease.
Several strengths and limitations should be noted when interpreting the results of our study.
A clear strength of this study is the large population-based cohort of pregnant women. Also,
the women’s anthropometric characteristics during early pregnancy were available, which
allowed us to evaluate the role of both total GWG and early GWG in relation to risk of HDP.
To our knowledge, we are only the second study to examine the association of early GWG with
the risk of HDP, and the first among Asian women. Several limitations of this study should
also be considered. First, though we assessed some potential confounding factors previously
reported to influence HDP, there were several other potential confounders that we were not
able to evaluate, such as smoking status and family history of HDP, because of the absence of
this information in our database. However, we note that the smoking prevalence of women in
China is very low [31] and we excluded women with a history of chronic hypertension or car-
diovascular disease prior to pregnancy from the study. Additionally, our study relies on a self-
reported pre-pregnancy weight, which may be under estimated. Although potential misclassifi-
cation bias may exist, previous studies suggest that the resulting BMI category from self-
reported data rarely alters, and the self-reported weight and height may be considered to be an
acceptable substitute for actual measurements [28, 32].
In conclusion, we conducted a large population-based cohort study in China to evaluate the
association of pre-pregnancy BMI and GWG with the risk of HDP, and found evidence that
pre-pregnancy BMI, total GWG, and early pregnancy GWG were all positively associated with
Pre-Pregnancy BMI, Gestational Weight Gain, and HDP
PLOS ONE | DOI:10.1371/journal.pone.0136291 August 25, 2015 8/10
risk of gestational hypertension and preeclampsia. Our results indicate that maternal over-
weight/obesity, early GWG, and total GWG should be considered in combination in targeting
and reducing the risk of HDP. Weight restrictions before and during pregnancy are both
important in the control of HDP, but weight gain reduction during pregnancy is much more
feasible.
Supporting Information
S1 Table. Associations of pre-pregnancy BMI, gestational BMI gain, and total GWG with
risk of subtypes of HDP (n = 84,656).
(DOCX)
S2 Table. Associations of GWG during early pregnancy (up to 18 weeks) with risk of sub-
types of HDP (n = 63,603).
(DOCX)
Acknowledgments
We are extremely grateful to Wuhan Health Bureau, and all the ho spitals and community
health centers involved in this study.
Author Contributions
Conceived and designed the experiments: BZ TZ. Performe d the experiments: RH SY LQ. Ana-
lyzed the data: CX CY WX. Contributed reagents/materials/analysis tools: Yiming Zhang AZ
SX ZQ. Wrote the paper: CX AZ BB ET YW Yaqi Zhang.
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