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Boys More Likely When Conception Takes Longer

Among women who took longer than a year to get pregnant, 57.6% had boys

MONDAY, Dec. 19 (HealthDay News) -- The longer it takes a woman to conceive, the more likely it is she will have a boy, according to a study in the Dec. 17 issue of the British Medical Journal.

Luc J. M. Smits, M.D., of Maastricht University in the Netherlands, and colleagues analyzed data for 5,283 Dutch women who gave birth to single babies between July 2001 and July 2003. The mean age of the women at conception was 30.5 years, and 83% of the pregnancies were planned.

Of the 498 women who took longer than 12 months to get pregnant, the probability of giving birth to a boy was 57.6% (287), the researchers found. By contrast, 51.1% of the 4,785 women who got pregnant faster had boys, suggesting that Y-bearing and X-bearing sperm swim at different speeds through viscous fluids.

For couples conceiving naturally, each extra year of trying to get pregnant is linked to an almost 4% higher probability of having a boy, the investigators found. The researchers did not find the same link in couples seeking medical help to get pregnant.

"The time taken to get pregnant is positively related to the chance of having a boy in couples conceiving naturally," the authors write.

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