Body mass index at 11-13 weeks' gestation and pregnancy complications in a Southern Chinese population: A retrospective cohort study.

Objective: To assess the association between body mass index (BMI) and adverse pregnancy outcomes. Materials and methods: A multicentre retrospective cohort study was conducted in three hospitals in Hong Kong including 67,248 women with singleton pregnancy at 11-13 weeks between 2010 and 2016. The relationship between maternal BMI and (1) miscarriage or stillbirth, (2) development of preeclampsia (PE), (3) gestational hypertension (GH), (4) development of gestational diabetes mellitus (GDM), (5) spontaneous preterm delivery (sPTD) <34 and <37 weeks, (6) delivery of a small for gestational age (SGA) or large for gestational age (LGA) neonate, (7) caesarean section (CS), and (8) postpartum haemorrhage (PPH) were examined after adjusting for confounding factors. Results: The prevalence of maternal overweight (BMI 25-29.9 kg/m(2)) and obesity (BMI >= 30 kg/m(2)) were 13.2% and 2.9%, respectively. Women with a BMI >= 30 kg/m(2) were nine times more likely to develop GH (95%CI 7.3-11.7), five times more likely to develop PE (95%CI 4.3-6.8) and GDM (95%CI 5.0-6.5) and 1.5-2 times more likely to deliver SGA/LGA neonate. sPTD, required delivery by CS and developed PPH, than those with a BMI of 18.5-22.9 kg/m(2), and that maternal underweight (BMI <18.5 kg/m(2)) significantly reduced the risk of GDM, delivery by CS, and PPH. Increased risk of subsequent development of adverse outcomes was observed when BMI was >= 23.0 kg/m(2). Conclusions: Maternal overweight and obesity are associated with an increased risk for subsequent development of various pregnancy complications. The need of increased awareness and health surveillance is essential when BMI >= 23 kg/m(2).