Maternal obesity and pregnancy outcome: a study of 287 213 pregnancies in London

OBJECTIVE: To examine the maternal and foetal risks of adverse pregnancy ou tcome in relation to maternal obesity, expressed as body mass index (BMI, k g/m(2)) in a large unselected geographical population. DESIGN: Retrospective analysis of data from a validated maternity database system which includes all but one of the maternity units in the North West Thames Region. A comparison of pregnancy outcomes was made on the basis of maternal BMI at booking. SUBJECTS: A total of 287 213 completed singleton pregnancies were studied i ncluding 176 923 (61.6%) normal weight (BMI 20-24.9), 79 014 (27.5%) modera tely obese (BMI 25 - 29.9) and 31 276 (10.9%) very obese (BMI greater than or equal to 30) women. MEASUREMENTS: Ante-natal complications, intervention in labour, maternal mo rbidity and neonatal outcome were examined and data presented as raw freque ncies and adjusted odds ratios with 99% confidence intervals following logi stic regression analysis to account for confounding variables. RESULTS: Compared to women with normal BMI, the following outcomes were sig nificantly more common in obese pregnant women (odds ratio (99% confidence interval) for BMI 25 - 30 and BMI greater than or equal to 30 respectively) : gestational diabetes mellitus (1.68 (1.53 - 1.84), 3.6 (3.25 - 3.98)); pr oteinuric pre-eclampsia (1.44 (1.28 - 1.62), 2.14 (1.85 - 2.47)); induction of labour (2.14 (1.85 - 2.47), 1.70 (1.64 -1.76)); delivery by emergency c aesarian section (1.30 (1.25 - 1.34), 1.83 (1.74 - 1.93)); postpartum haemo rrhage (1.16 (1.12 - 1.21), 1.39 (1.32 - 1.46)); genital tract infection (1 .24 (1.09 - 1.41), 1.30 (1.07 - 1.56)); urinary tract infection (1.17 (1.04 - 1.33), 1.39 (1.18 - 1.63)); wound infection (1.27 (1.09 - 1.48), 2.24 (1 .91 - 2.64)); birthweight above the 90th centile (1.57 (1.50 - 1.64), 2.36 (2.23 - 2.50)), and intrauterine death (1.10 (0.94 - 1.28), 1.40 (1.14 - 1. 71)). However, delivery before 32 weeks' gestation (0.73 (0.65 - 0.82), 0.8 1 (0.69 - 0.95)) and breastfeeding at discharge (0.86 (0.84 - 0.88), 0.58 ( 0.56 - 0.60)) were significantly less likely in the overweight groups. In a ll cases, increasing maternal BMI was associated with increased magnitude o f risk. CONCLUSION: Maternal obesity carries significant risks for the mother and f oetus. The risk increases with the degree of obesity and persists after acc ounting for other confounding demographic factors. The basis of many of the complications is likely to be related to the altered metabolic state assoc iated with morbid obesity.