Women who are an unhealthy weight during their first pregnancy might have a false sense of security if their babies are born with no complications. But a new study out of Saint Louis University suggests complications can still arise when the women get pregnant for a second time — even if, by then, they have reached a healthy weight.
Using data from the maternally linked Missouri birth registry, the researchers identified women in Missouri who gave birth to their first two children between 1989 and 2005. They only included women who did not have any chronic health problems like diabetes or hypertension, and who had no complications with their first birth.
Of the 121,049 remaining women in the study sample, about 89 percent were white and 11 percent were African American. The researchers then compared women who were a healthy weight to those who were not.
Graduate student Maya Tabet was part of the Saint Louis University research team led by epidemiologist Jen Jen Chang. Tabet said they found that women who were underweight (defined as having a body mass index, or BMI, under 18.5), overweight (BMI greater than or equal to 25) or obese (BMI greater than or equal to 30) prior to their first pregnancy had a higher risk of complications the second time they got pregnant. "And some of the risk, or most of the risk, remained present and remained significant, even if those women reached a normal weight by their second pregnancy," Tabet said.
Specifically, compared to women who were a healthy weight prior to their first pregnancy:
- Women who were underweight had a 20 percent higher risk of preterm birth and a 40 percent higher risk of having babies who were small for their gestational age during their second pregnancy.
- Women who were overweight had an 18 percent higher risk of having babies who were large for their gestational age; a 72 percent higher risk of preeclampsia (high blood pressure and other complications); and were 39 percent more likely to have a cesarean delivery during their second pregnancy.
- Women who were obese had a 55 percent higher risk of having babies who were large for their gestational age; a 156 percent higher risk of preeclampsia; and were 85 percent more likely to have a cesarean delivery during their second pregnancy. They were also 37 percent more likely to have their second baby die within the first 28 days after birth.
Tabet said the reasons why those risks persisted — even for women who had achieved a healthy weight by their second pregnancy — is not yet clear. "But we do suspect that some of the physiological changes that happen because of having an unhealthy weight in the first pregnancy — some of those changes may be permanent, and they might affect negatively the second pregnancy and subsequent pregnancies as well," Tabet said.
From a public health perspective, Tabet finds these results troubling. "Because what we're saying is that even if women reach a healthy weight by their second pregnancy, they would be at increased risk of complications just because they started their first pregnancy with an unhealthy weight."
Tabet said the findings highlight the need for women to be at a healthy weight the first time they get pregnant — and if they're not, for them to take extra care during subsequent pregnancies, even if all goes well with the first.
According to the U.S. Centers for Disease Control and Prevention, about 5 percent of women in the United States start a pregnancy underweight, and more than 50 percent are either overweight or obese.
The Saint Louis University study was published online in the American Journal of Obstetrics & Gynecology.