Time of Pregnancy Determines Gender
Reported December 16, 2005
(Ivanhoe Newswire) — Researchers say the longer it takes a woman to get pregnant, the more likely it is she’ll have a boy.
Researchers analyzed data for 5,283 women who gave birth to single babies. The 498 women who took longer than 12 months to get pregnant had a 58-percent chance of having a boy, whereas the proportion of male births among the 4,785 women with shorter times to pregnancy was only 51 percent.
Researchers say for each additional year of trying to get pregnant, couples conceiving naturally have nearly a 4-percent higher chance of conceiving a boy after adjusting for factors like age, smoking status, alcohol use and variability of the menstrual cycle.
The findings may explain why more boys than girls are born despite the fact that human semen holds equal amounts of X bearing and Y bearing sperms — X chromosomes being girls and Y chromosomes being boys. In most countries, 105 boys are born for every 100 girls.
Investigators say the findings support the idea that, in thick fluids, sperms bearing the Y chromosome swim faster than those bearing the X chromosome. Women whose cervical mucus is relatively thick would not only have more difficulties conceiving naturally but also a higher probability of male offspring if they do get pregnant.
SOURCE: The British Medical Journal, 2005;331:1437-1438
