Pregnant women who are overweight or obese in the first trimester of pregnancy and those who have a greater change in body weight during pregnancy are more apt to have lengthier pregnancies and more complications, according to results of a new study.

Dr. Fiona C. Denison, of the University of Edinburgh, UK, and colleagues analyzed data from the Swedish Medical Birth Register on women who gave birth between 1998 and 2002.

Out of 143,519 pregnancies, 6.8 percent were delivered “postdate” - defined as longer than 42 weeks. A normal pregnancy lasts 40 weeks.

Compared with women with normal body mass indexes (BMIs), more women with higher BMIs during the first trimester, as well as those with greater weight gain during pregnancy, had longer-than-normal pregnancies.

Being overweight or obese during the first trimester was also associated with a lower chance of spontaneous delivery at term and being obese was associated with a higher risk of stillbirth, pregnancy-related (gestational) diabetes and need for cesarean delivery.

“Maternal obesity poses a significant risk to maternal and fetal health during pregnancy, and our study confirms the findings of others that obesity is associated with significant complications including stillbirth, gestational diabetes, pregnancy-induced hypertension and cesarean section,” Denison’s team concludes.

“If a healthy lifestyle including physical activity and healthy eating, which are more common in underweight women, were advocated more strongly for the obese obstetric population,” they suggest, “then obstetric outcomes might be improved.”

SOURCE: British Journal of Obstetrics and Gynecology, May 2008.