Fertility treatment may produce fewer baby boys

The number of baby boys conceived by a fertility treatment known as ICSI may be lower than what is produced by Mother Nature, a new study suggests.

On average, there are 105 baby boys born for every 100 girls -- a natural advantage that helps balance out the higher number of deaths among male fetuses and infants. But in the new study, researchers found that this male-to-female birth ratio seems to be reversed when infants are conceived through intracytoplasmic sperm injection, or ICSI.

Among more than 15,000 U.S. babies born in 2005 via assisted reproduction, the investigators found that a particular ICSI approach appeared to result in a smaller-than-average number of boys.

The effect was seen when ICSI was performed using blastocyst-stage embryos -- where embryos are allowed to mature a couple days longer than the traditional norm before they are transferred to the mother. This allows doctors to transfer fewer embryos, reducing the odds of couples having triplets or higher-order births.

Among couples undergoing this procedure, just under 50 percent of births were boys. That compared with a U.S...