Heavier Mothers May Have More Boys

Want a baby boy? Eat more.

A significant increase in the weight of a mother before pregnancy may affect the gender of the child, according to a recent study conducted by researchers at the Harvard School of Public Health (HSPH) and the Karolinska Institutet in Stockholm, Sweden.

The results of the study indicate that mothers who increased their body mass index substantially between the first and second pregnancies were more likely to give birth to a baby boy the second time around.

“A phenomena may be occurring,” said the study’s lead author Eduardo Villamor, an assistant professor of international nutrition at HSPH. “These results are provocative because there are not many factors known to influence the sex ratios of the child,” and this study could lead researchers to further discoveries regarding possible gender prediction, he said.

The study sampled 220,889 women picked from the Swedish Birth Registry, who were divided into three groups: those who had lost weight, gained weight, or stayed the same weight between pregnancies.

According to Villamor, among women who had neither gained nor lost weight between pregnancies, 52 more boys than girls were born per 1,000 babies. But in the group of women who had gained 3 BMI units or more, 80 more boys than girls were born per 1,000 babies.

Hannia Campos, senior lecturer on nutrition at HSPH, said gaining weight before pregnancy poses risks.

“Increased weight could have several adverse pregnancy-related outcomes, including [an] increase in the chances of a woman having a cesarean delivery or stillbirth,” she said.

Villamor said that the study, which appeared in the Sept. 24 issue of Fertility & Sterility, is “unlikely to have a demographic impact on a larger level.”

“[The study] does imply that there are other things at work that we don’t know about” regarding the factors that contribute to the sex of a child.”