TUESDAY, July 28, 2015 (HealthDay News) -- Women with an unhealthy weight in a first pregnancy could be at greater risk for complications in their next pregnancy -- even if they're at a good weight, a new study finds.
Most American women are not at a healthy weight when they first become pregnant, meaning their body mass index (BMI) is higher or lower than ideal, researchers say. It is more common for them to have a high BMI than a low one. BMI is an estimate of body fat based on height and weight.
For the study, researchers looked at data from more than 121,000 women in Missouri who gave birth between 1989 and 2005.
Those who were underweight during their first pregnancy were 20 percent more likely to give birth early and 40 percent more likely to have a small-for-gestational-age baby during their second pregnancy, compared to women with a healthy weight during their first pregnancy.
Women who were obese during their first pregnancy were 54 percent more likely to have a large-for-gestational-age baby during their second pregnancy. In addition, they were 156 percent more likely to have a dangerous complication of pregnancy called preeclampsia, and 85 percent more likely to have a cesarean delivery. Also, their babies were 37 percent more likely to die within 28 days after birth, the study found.
The study was published online June 20 in the American Journal of Obstetrics and Gynecology.
"While moms who weigh too much or too little might have uncomplicated pregnancies and deliver healthy babies the first time around, our research shows they are still at increased risk of adverse outcomes during their second pregnancies. That risk may not go away even if they are at a normal weight when they get pregnant again," study senior author Jen Jen Chang, associate professor of epidemiology at Saint Louis University, said in a university news release.
"The bottom line for physicians and second-time moms is not to let down their guard even if things went well for moms with unhealthy weight during the first pregnancy, or if those moms reach a normal weight when they become pregnant again," she added.
It's not known why women with unhealthy weight but no complications during a first pregnancy might be at increased risk during their second pregnancy.
"I suspect our body remembers, but we don't know for certain," Chang said. "Women who are over- or underweight during their first pregnancy may experience permanent physiological changes that negatively affect their second baby."
Experts agree that maintaining a healthy weight is the best way to ensure a healthy pregnancy.
The Academy of Nutrition and Dietetics has more about healthy weight during pregnancy.