Higher BMI in pregnant women associated with a greater likelihood of pre-eclampsia, caesarian delivery and higher offspring birth weight and body fat

Abstract

ContextAlthough there are several published reports establishing the association of maternal obesity with adverse pregnancy outcomes, few explore these associations independent of glycaemia. Previous research on this topic have either not reported data on blood glucose levels or confi ned the analysis to women without recorded gestational diabetes. This leaves a large group of pregnant women who have impaired glucose tolerance but not quite clinically diagnosed gestational diabetes whose risks in pregnancy remain poorly understood. The HAPO (Hyperglycaemia and Adverse Pregnancy Outcome) study aimed to describe any adverse outcomes in these women. As part of this epidemiological investigation, accurate data on height and weight of women were collected and utilised in the present analysis to assess the risk of adverse pregnancy outcomes in obese women independent of their glycaemic status. MethodsThis prospective cohort study was based in 15 centres in nine countries in order to recruit a multicultural ethnically diverse population. Maternal body mass index (BMI) was calculated from height and weight recorded at the time of administration of the oral glucose tolerance test, typically between 24 and 32 weeks of gestation. BMI was used in the analysis as a continuous variable and as categories as recommended by the WHO criteria.Primary outcomes assessed were birth weight for gestational age >90th percentile, delivery by primary caesarean section, neonatal hypoglycaemia and cord serum C-peptide >90th percentile. Secondary outcomes included were maternal pre-eclampsia, preterm delivery before 37-week gestation and neonatal adiposity. Shoulder dystocia or birth injury, neonatal hyperbilirubinaemia and admissions to neonatal intensive care units were also reported.Although recruitment continued over 5 years, the follow-up period was from the time of OGT testing in the third trimester to delivery of the baby. Neonatal follow-up was up to 72 h after delivery. FindingsThis report demonstrates that both maternal BMI as well as glycaemic status are independently associated with selected adverse outcomes of pregnancy. A higher birthweight centile was positively associated with maternal BMI with a 12% increase in risk of macrosomia from the lowest BMI group (3.9%) to that in the highest (15.9%). Primary caesarean delivery was also more common in women with higher BMI; the risk increased in a dosedependent manner with increasing maternal BMI.In the case of neonatal hypoglycaemia and hyperinsulinaemia (measured by cord C-peptide), the results showed a similar pattern of association with increasing maternal BMI. Commentary on: HAPO Study Cooperative Research Group. Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) Study: associations with maternal body mass index. BJOG 2010;117:575-84.