SCIENCE / MEDICINE : Sex Selection in Test Tube

Scientists at Hammsmith Hospital in London say they have been able to select 3-day-old test-tube embryos that are destined to become girls and implant them in women, including two who are expecting twins this summer. Further research might provide a way to screen out embryos that would be expected to develop serious genetic diseases, removing the prospect of abortions in those cases, researchers said.

The study was aimed at producing female babies in cases where a male could inherit one of the 200 serious genetic diseases that affect only males, said researcher Alan Handyside.

The embryo analysis involves collecting eggs from a woman, fertilizing them in a test tube and letting them grow to eight-cell embryos. A single cell is removed from each embryo to see if it contains a bit of genetic material that indicates the presence of a Y chromosome, which would mean the embryo is destined to become a boy.