Even before the first baby is born, it is important for women of childbearing years to maintain a healthy body mass index (BMI). A woman’s weight at the onset of her first pregnancy influences the health of the pregnancy and the baby she carries. A new study indicates that even Baby #2 is affected when mom carries too little or too much weight at the beginning of her first pregnancy.

“I suspect our body remembers,” said Dr. Jen Jen Chang, associate professor of epidemiology at Saint Louis (Missouri) University (SLU), although the mechanisms for transferring risk from one pregnancy to the next remain unclear. Chang is senior author of the research paper published online on June 20 by the American Journal of Obstetrics and Gynecology.

Chang and her team of researchers analyzed data gleaned from birth registries that contained maternal medical information on 121,092 women in Missouri between 1989 and 2005. When these women first became pregnant, their BMI fell into the underweight, healthy, and overweight/obese ranges; all experienced an uncomplicated pregnancy and all had healthy firstborn children.

Women who are underweight or overweight during pregnancy face greater risks of pregnancy-related complications such as preterm birth, preeclampsia, and even infant death than women who enter and maintain pregnancy at a healthy weight. When the SLU research team compared the outcomes of second pregnancies on the study group, they found that:

Women underweight at the beginning of their first pregnancy were:

  • 20% more likely to have a preterm birth during second pregnancy than women at healthy weight during their first pregnancies.
  • 40% more likely to deliver a second baby small for gestational age.

Women overweight at the beginning of their first pregnancy were:

  • 37% more likely to experience neonatal death during the second pregnancy.
  • 54% more likely to deliver a second baby large for gestational age.
  • 85% more likely to require cesarean delivery.
  • 156% more likely to develop preeclampsia.

The risks during second pregnancy reflected the risks the women faced according to their weight at the outset of their first pregnancy. This risk factor remained even when the woman was at a healthy weight at the outset of the second pregnancy.

Chang suggests “Women who are over or underweight during their first pregnancy may experience permanent physiological changes that negatively affect their second baby.” The research team considers this possibility a public health concern since as many as 17,000 babies die each year in the United States during their first month of life.

The SLU research team would like to see healthcare professionals routinely encouraging women of childbearing age to maintain a healthy weight before a first pregnancy and throughout reproductive years to ensure the safest pregnancies and healthiest babies possible.


  1. Tabet, Maya. "Prepregnancy body mass index in a first uncomplicated pregnancy and outcomes of a second pregnancy." AJOG / American Journal of Obstetrics & Gynecology (2015). Elsevier Inc.. Web. 4 Aug. 2015.
  2. "Body Mass Index (BMI)." CDC / Division of Nutrition, Physical Activity, and Obesity. US Department of Health & Human Services, 15 May 2015. Web. 4 Aug. 2015.