Introduction
Maternal overweight and obesity has drawn worldwide attention
increasingly in recent years. The data from the 2011-2012 US National
Health and Nutrition Examination Survey (NHANES) showed that the
prevalence of obesity in women aged 20-39 years was 31.8% in the United
States1. Furthermore, based on the data of single term
nulliparous, 48% and 24% of the pre-pregnant women were overweight or
obesity in the US and Germany, respectively. In UK, about one quarter of
pregnant women or women aged over 20 years were obesity according to the
European Peristat Database and WHO data. However, in Asia, the
proportion of obesity among women in childbearing age is not as high as
those in the western countries. Such as in South Korea, less than 10%
of women in reproductive age
were
classified as obesity with body mass index (BMI) more than 30 kg/m². The
similar condition is found in China, especially in south China. Even
though the WHO’s lower definitions for Asia-specific (overweight: BMI≥23
kg/m2; obesity:
BMI≥25
kg/m2) were used, only 15.8% of Hong Kong Chinese
pregnant women were classified as obesity at the first visit. Although
some studies reported that 10%–24% of pregnant women were overweight
or obesity in China2 the phenomena of underweight is
also common with almost 11%–13% of women in China were underweight.
This proportion is nearly equal to the overweight and obesity.
Increasing risks of gestational diabetes mellitus (GDM), gestational
hypertension (GH), pre-eclampsia (PE) and caesarean section et al. were
associated with increasing BMI in the Chinese pregnant population, which
were similar to the Caucasian studies. Considering the prevalence of
obesity in China is lower than those in the western countries, the risks
of GDM and other complications should be decreased in Chinese pregnant
women. However, the facts are on the contrary. The occurrence rate of
GDM is relatively higher than those in many western countries in spite
of the larger proportion of underweight and normal weight pregnant women
in China. Whether the factors related to GDM and other complications in
the underweight group are different from those in the overweight/obese
women group need to be addressed.
Increasing evidences have been found to pronounce the positive
association between dyslipidemia and adverse pregnancy outcomes such as
GDM and large for gestational age (LGA). Markedly elevated triglyceride
(TG) levels were found throughout the course of pregnancy in GDM, while
high-density lipoprotein cholesterol (HDL-C) levels were reduced in the
late course of pregnancy. In a large community-based cohort study, serum
TG levels in the first trimester of pregnancy were demonstrated to
positively associated with adverse maternal (gestational hypertension,
GH and preeclampsia, PE) and fetal (LGA) outcomes3. In
addition, a larger retrospective study in China showed that early
pregnancy total cholesterol (TC) level was an independent risk factor
for GDM, TG level was independently associated with the prevalence of
GDM and PE, and low-density lipoprotein cholesterol (LDL-C) level was
significantly associated with the risk of GDM and preterm birth.
However, rare studies concerned about whether the associations of the
maternal and fetal morbidity with lipid profiles are different in
different pre-gestational BMI categories. Among pregnant women with
obesity, differences in metabolic profile, including exaggerated
dyslipidaemia, were evident at least 10 weeks prior to a diagnosis of
GDM in the late second trimester 4. Nevertheless,
whether the relationship is specific to the underweight pregnant women
has not been well investigated to date.
Therefore, a prospective cohort study was performed to evaluate the
correlations between maternal lipid profiles and adverse pregnancy
outcomes after grouping pregnant women by pre-pregnant BMI as
underweight, normal weight and overweight/obese women. We specifically
assess the predictive value of lipid profiles on the risks of GDM, LGA
and other adverse pregnancy outcomes in the underweight pregnant group.