Overweight and obese moms face more risk of early births

“It looks like the heavier the woman, the higher the risk,” said Dr. Sarah McDonald, associate professor in the Michael G. DeGroote School of Medicine's Department of Obstetrics and Gynecology. She led a meta-analysis of 84 studies comparing overweight and obese to normal weight women.

The analysis found overweight or obese women have a 30 per cent greater risk of induced preterm birth before 37 weeks and that risk climbs to 70 per cent for very obese women. (A full-term pregnancy is 40 weeks).

Overweight or obese women also had a higher risk of early preterm birth – before 32 or 33 weeks, again with higher risks in heavier women. The research appears in the latest issue of the British Medical Journal (BMJ).

“Preterm birth and low birth weight are leading predictors of neonatal morbidity and mortality and morbidity or illness through childhood,” said McDonald, adding there are also implications for the child's family and the health care system.

She said it is not yet clear why there is a link between a mother's weight and preterm birth.

Overweight and obesity is now the most common pregnancy complication in many developed, and some developing countries. Statistics Canada reports 29 per cent of Canadian women are overweight and 23 per cent are obese.

Two-thirds of Hamilton area women who are pregnant are overweight or obese, according to local data. No similar provincial or national statistics are available.

McDonald said the popular view that a pregnant woman is eating for two is not true. “It's just not right. Typically, women should add about 300 calories a day – the equivalent of a large glass of milk and a piece of fruit – in the latter half of their pregnancy,” she said.

Counselling women before they become pregnant on the potential risks to overweight and obesity using a multi-pronged approach is required, McDonald said.

“Family doctors, nurses, obstetricians, public health nurses, and dieticians are all important in delivering a consistent message. Women often make many positive lifestyle changes for their pregnancies to have healthier babies, so now we need to make sure that they are aware of these findings so they can optimize their weight before pregnancy.”

The research was supported by a Canadian Institute of Health Research (CIHR) operating grant. McDonald is supported by a CIHR New Investigator Award.