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 over-stimulate 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 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.

They were asked about pre-implantation genetic diagnosis, or PGD, which can be done as part of in vitro fertilization, when eggs and sperm are mixed in a lab dish and the resulting embryos implanted directly into the womb. In PGD, a single cell from an embryo that is three to five days old is removed to allow its genes and chromosomes to be analyzed.

About 1 of every 20 in vitro pregnancy attempts in the United States last year used PGD, the survey found.

Two-thirds of the time it was to detect abnormalities that would keep the embryo from developing normally and doom the pregnancy attempt.

In 12 percent of cases, PGD 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 PGD said they had done so for non-medically related sex selection. Nearly half of those clinics said they would only offer sex selection for a second or subsequent child.

“That’s really startling,” University of Pennsylvania ethicist Arthur Caplan said of the high number of PGD 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.

One doctor who offers it takes a different view.

“It performs a much desired service. We’re making people happy,” said Dr. Jeffrey Steinberg, medical director of Fertility Institutes, which has clinics in Los Angeles, Las Vegas and Guadalajara, Mexico.

Many countries ban PGD or restrict it to prevention of serious inherited diseases. Many people from foreign countries travel to the United States to obtain it, especially from countries like China and Canada.

Baruch said the survey was intended to get a realistic view of what was going on.

“This is the first time anyone has tried to quantify how often PGD is done and what it’s being offered for,” she said.