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Researchers at the University of New South Wales reviewed the records of approximately 13,400 babies born in Australia and New Zealand since 2006 whose parents used in vitro fertilization and found that 56.1 percent of the children were boys.
"When you convert that to sex ratio at birth, that's around 128 boys to 100 girls -- that's quite significant," Jishan Dean, a doctoral student who participated in the research, told the Australian Associated Press.
The study, published in BJOG: An International Journal of Obstetrics and Gynaecology, does not offer an explanation as to why in vitro fertilization, or IVF, seems to increase the odds of having a boy.
As of 2006, an estimated 3 million children had been born with the assistance of IVF since Louise Brown became the world's first so-called test-tube baby in 1978.
In the past three decades, IVF birth rates have gone up markedly, and the procedure has steadily gained in popularity for couples unable to reproduce naturally. In Australia, for instance, the number of babies born using IVF doubled from 2004 to 2008, a report by the Australian Institute of Health and Welfare found. Over that same period, however, Australian women who had undergone fertility treatment of some kind had much higher rates of delivering via cesarean section.
According to statistics from the American Pregnancy Association, the live birth rate for women in the United States who undergo IVF varies according to age. While 30 percent to 35 percent of women under age 35 successfully deliver a child, only 6 percent to 10 percent of women over age 40 do.
Here's a handy video that explains how IVF works.
