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.