Being overweight years before pregnancy linked to bigger babies

Women who become overweight or obese during the transition from adolescence to adulthood are significantly more likely to give birth to babies with excessive birth weights, according to a new study published in the Journal of Adolescent Health.

Researchers know that a woman’s health during pregnancy can have a potent effect on the health of her baby, explain study authors Kelly Strutz, M.P.H., Liana Richardson, Ph.D., and Jon Hussey, Ph.D., of the University of North Carolina at Chapel Hill. However, says Strutz, little research has examined the effects of a mother’s health long before she becomes pregnant on the future health of her babies. The few studies that exist mainly look at the mother’s health immediately preceding conception.

The researchers reviewed data from 3,400 births to female participants in the National Longitudinal Study of Adolescent Health (Add Health). Add Health is following a national cohort of over 15,000 women and men first interviewed in 1994-1995, when they were between the ages of 11 and 19. Since then, Add Health has collected new health information from the same group, with the last contact when participants were between the ages of 24 and 32, a time when many were already parents.

The scientists examined whether behaviors such as heavy drinking, smoking, exercising, or maintaining a healthy body mass index (BMI) in the years before these women became pregnant influenced the birth weight of their babies, a general indicator of newborn health. Results showed that only the mother’s BMI appeared to affect her baby’s birth weight.

While Strutz cautions that more research is needed, she notes that the study offers potentially encouraging news on several preconception health behaviors, suggesting that smoking or heavy drinking long before pregnancy may not affect a baby’s birth weight if a mother amends these behaviors before pregnancy. However, she adds, the findings also emphasize the importance of women maintaining a healthy weight over the long-term, not just during pregnancy itself.

“If you pick up these risk factors for women earlier in life,” she said, “you have a greater opportunity to try to modify and improve them before they even start to have children.”

According to Sebastien Bouret, Ph.D., a researcher at Children’s Hospital Los Angeles, findings from his lab and others suggest that the fallout from excessive birth weight may extend far beyond a single generation. “The problem we have is that this is sort of a vicious cycle,” he says. “Babies born to obese mothers are at a higher risk of becoming obese themselves, and when they’re at an age to reproduce, they are also obese and give birth to babies at risk of obesity.”

“This paper suggests that we need intervene early on,” he says, “in adolescence, long before women become pregnant.”