Research News

Higher risk of preterm delivery in overweight and obese women

BMJ 2013; 346 doi: (Published 12 June 2013) Cite this as: BMJ 2013;346:f3793


Women who are overweight or obese in early pregnancy have an increased risk of delivering early. A large Swedish study of more than one and a half million singleton pregnancies reported a steady increase in preterm deliveries with rising maternal body mass index (BMI), and the link was particularly strong for deliveries before 27 weeks’ gestation.

Overweight or obesity was associated with spontaneous preterm deliveries before 27 weeks and with preterm deliveries that were medically indicated at any gestation up to 36 weeks. Odds were increased even for women with a BMI between 25 and 30. Women with a BMI of 40 or more at the beginning of pregnancy were four times more likely to need a caesarean section or induction before 32 weeks than women of normal weight. They were also twice as likely to need delivering between 32 and 36 weeks. Most extra preterm births that were medically indicated were due to complications of pregnancy, such as diabetes and pre-eclampsia. Associations disappeared or were substantially attenuated in analyses that excluded women with these obesity related problems. All analyses were adjusted for maternal age, parity, smoking, education, height, and country of birth.

Being born too early is a leading cause of neonatal and infant death. Survivors can be left with lifelong disability, say the authors. These findings have serious public health implications in Sweden and probably elsewhere. In the US, where rates of preterm birth are twice as high, more than half of all women are overweight (26%) or obese (27.4%) at the start of pregnancy.


Cite this as: BMJ 2013;346:f3793