Weight gain between first and second pregnancies associated with increased odds of male se...(pregnancies between 1992 and 2004 (live ...)

Date:9/24/2007

pregnancies between 1992 and 2004 (live births and stillbirths were included). The researchers analyzed the change in womens body mass index (BMI) between the first and second pregnancies. (BMI is weight in kilograms divided by the square of height in meters.) The male to female sex ratio of the second pregnancy increased linearly with the amount of weight change from the first to second pregnancy, from 1.024 in women who lost more than 1 unit BMI to 1.080 in women who gained 3 or more units (a male to female sex ratio of 1.000 would indicate an equal number of boys and girls being born). The trend was independent of obstetric complications, maternal smoking, parental age, length of the interpregnancy interval and the sex or survival status of the first-born child.

The data suggest that interpregnancy weight gain appears related to a slight increase in the probability of giving birth to a baby boy during a second pregnancy. The obesity epidemic does not appear to explain the observed decline in the sex ratio in some industrialized countries, which indicates that there are factors still unknown influencing the probability of giving birth to boys or girls.

The authors are careful to note that women should not gain weight to try to influence the sex of their baby. Weight gain before pregnancy carries significant risks to the mother and the baby, and should not be practiced to influence the odds of having a boy, said Villamor. Other factors of which weight gain is only an indicator could be at play here.

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Contact: Todd Datz tdatz@hsph.harvard.edu 617-432-3952 Harvard School of Public Health Source:Eurekalert

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