Boy or girl? Almost half of U.S. fertility clinics that offer embryo screening say they allow couples to choose the sex of their child, the most extensive survey of the practice suggests.

Sex selection without any medical reason to warrant it was performed in about 9 percent of all embryo screenings last year, the survey found.

Another controversial procedure - helping parents conceive a child who could supply compatible cord blood to treat an older sibling with a grave illness -was offered by 23 percent of clinics, although only 1 percent of screenings were for that purpose in 2005.

For the most part, couples are screening embryos for the right reasons - to avoid passing on dreadful diseases, said Dr. William Gibbons, who runs a fertility clinic in Baton Rouge, La., and is president of the Society for Assisted Reproductive Technology, which assisted with the survey.

"There are thousands of babies born now that we know are going to be free of lethal and/or devastating genetic diseases. That's a good thing," he said.

However, the survey findings also confirm many ethicists' fears that Americans increasingly are seeking "designer babies" not just free of medical defects but also possessing certain desirable traits.

"That's a big problem if that's true," Boston University ethicist George Annas said of the sex selection finding. "This is not a risk-free technique," he said referring to in vitro fertilization, which can overstimulate a woman's ovaries and bring the risk of multiple births.

"I don't think a physician can justify doing that to a patient" for sex selection alone, Annas said.

Survey results were published on the internet on Wednesday by the medical journal Fertility and Sterility and will appear in print later.

The survey was led by Susanna Baruch, a lawyer at Johns Hopkins University's Genetics and Public Policy Center in Washington, D.C., with the cooperation of the reproductive medicine society. It involved an online survey of 415 fertility clinics, of which 190 responded.

The genetic screening is called pre-implantation genetic diagnosis, or PGD, a process in which a cell is taken from an embryo that is three to five days old and isn't yet implanted in a woman. That cell's genes and chromosomes are then analyzed.

Two-thirds of the time when people chose to have an embryo's genes analyzed, it was to detect abnormalities that would keep the embryo from developing normally and doom the pregnancy attempt.

In 12 percent of cases, the screening was used to detect single-gene disorders like those that cause cystic fibrosis. Three percent of cases were to detect problems that mostly affect males, because they have only one copy of certain genes.

However, these cases are different from those done purely for gender preference. A whopping 42 percent of clinics that offer the screening said they had done so for non-medically-related sex selection. Nearly half of those clinics said they would offer sex selection only for a second or subsequent child.

"That's really startling," University of Pennsylvania ethicist Arthur Caplan said of the high number of genetic screenings for sex selection alone. "Family balancing seems like a morally persuasive reason to some people," but doing gender selection just because a couple doesn't want any girls, or any boys, is troubling, he said.

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