One of the strongest known risk factors for spontaneous or unexpected preterm birth – any birth that occurs before the 37th week of pregnancy, most often without a known cause – is already having had one. For women in this group who would like to avoid this scenario in their second pregnancy, focusing on weight gain and dietary changes may not be the best strategy. A new study reported at the Society for Maternal-Fetal Medicine’s annual meeting found no connection between weight gain and the risk of repeat preterm birth.
Study author David Hackney, M.D., a high-risk pregnancy expert in the Department of Obstetrics and Gynecology at the University of Rochester Medical Center, says women who’ve had a prior preterm birth should talk with their doctor about the level of weight gain that is right for them, but, in general, should follow standard weight gain guidelines during their second pregnancy.
Hackney, who treats many women who’ve gone through early labor and delivery, wanted to zero in on weight gain because women have a certain degree of control over it. While there are some modifiable risk factors for preterm birth, including smoking, drinking and illicit drug use, understanding more about how women and their physicians can work together to reduce risk is a high priority, since all preterm babies are in danger of significant health problems at birth and beyond.
“Usually, weight gain and being overweight or obese is protective against spontaneous preterm birth. In fact, the risk of unexpected labor and delivery is 20 percent lower in obese than non-obese women,” said Hackney. “We’d hoped to find that women were at greater risk of repeat preterm birth if they had a lower rate of weight gain in their second pregnancy, meaning patients could potentially decrease their risk by ensuring they gained an appropriate amount of weight. But, our research suggests you can’t alter risk through changes in weight or diet.”
According to the Centers for Disease Control and Prevention, more than half a million babies in the United States – one in every eight – are born premature each year. Premature babies are more likely to have brain, breathing and digestive problems, and are at risk for developmental and learning problems later in life.
The study included 166 women who delivered their first and second babies at the University of Rochester Medical Center between 2004 and 2010. All participants delivered their first baby preterm, and close to 29 percent delivered their second baby preterm as well.
Researchers analyzed the amount of weight women gained from the beginning of both pregnancies through 24 to 28 weeks, roughly the end of the second trimester, taking into account age, pre-pregnancy body mass index (BMI), tobacco use and how early the participants delivered in their first pregnancy. They did not include weight gain in the third trimester because not all women made it through part or even any of the last trimester before they delivered.
Patients who delivered their second baby preterm were younger and had their first baby much earlier than women who went on to deliver their second baby at term (sometime after the 37th week of pregnancy). First and second trimester weight gain did not influence the likelihood of a repeat spontaneous preterm birth.
Hackney says the study is unique because of the wide breadth of information researchers used – weight gain in the first pregnancy, weight gain between the first and second pregnancy, and weight gain in the second pregnancy. Other studies on the topic haven’t benefitted from such a thorough set of data, for example, relying on weight gain information from only one pregnancy.
In addition to Hackney, Danielle Durie, M.D., a former maternal-fetal medicine fellow at the Medical Center, now at Lehigh Valley Hospital in Allentown, Pennsylvania, and Radhika Tirumala, M.D., of Rochester General Hospital, also contributed to the research.