Interpregnancy Weight Gain May Increase the Odds of Having a Boy

People are always interested to know if there are any factors that influence the likelihood of having a boy or a girl. Statisticians analyze data available on births to find trends. Researchers try and associate these trends with factors. However, there is usually no connection. That is until now. A new study from the Harvard School of Public Health may have found at least one connection. According to the study, mothers who gain weight between pregnancies have a slightly higher probability of giving birth to a boy during the subsequent pregnancy.

The study can be considered monumental, to say the least. There have been many studies done in the past that attempted to find a link been certain factors and the birth sex ratio. However, few have been found. Among those that have been found, most of them demonstrate weak causality. Few biological factors are known to influence the likelihood of having a boy or girl. Any time there is a link found, it is extremely important.

The study looked at data from the Swedish Birth Registry. It included more than 200,000 women who had two or more pregnancies between 1992 and 2004. The researchers looked at changes in body mass index (BMI) among the women. They were particularly interested in changes in BMI between pregnancies. Researchers found that the male to female sex ratio of subsequent pregnancies increased linearly with BMI increases between pregnancies. Basically, the more a women gained between pregnancies, the higher her chances of giving birth to a boy in the subsequent pregnancies. This trend held true even when other factors were accounted for including smoking and maternal age.