To cut down on multiple births, the American Society for Reproductive Medicine Thursday recommended that its 9,000 specialists reduce the number of embryos they implant in women undergoing assisted reproduction -- a response to the alarming growth in twins, triplets and quadruplets that result when a larger-than-expected number of embryos "take" after being implanted in the womb.

The society recommended that its members implant a maximum of two embryos in women under 35 who have "an especially good prognosis" for getting pregnant, and a maximum of three embryos for women who have a good prognosis. "Most people view twins as a wonderful opportunity. But the reality of potential complications [from multiple births] is a little sobering," says ASRM's president, R. Jeffrey Chang.

The fertility industry has always been the high frontier for medical cowboys. The government and insurers have largely steered clear of the baby-making trade, leaving it to the outsized egos willing to step in for Mother Nature in the fundamental act of creation.

But Thursday's announcement reflects rising concern about the practices of fertility specialists. In 1995 Congress began requiring fertility clinics to publish their success rates. Patient advocates are having some success lobbying for insurance coverage of fertility treatments. And specialists have started to respond to accusations that their practices can endanger the very kids they were hired to help produce.

Each year in America, about 10,000 children are born as a result of in vitro fertilization and related techniques -- and about a third of them are twins. Another 7 percent are triplets, with a few dozen quadruplets and a handful of quintuplets.

For triplets and higher-order multiples, the moral and financial costs are high. Women aren't designed to carry litters, and these children frequently are born prematurely and can suffer enduring medical problems -- brain and lung damage, digestive ailments. Their difficult lives can ruin the families that were so eager to have them. And although fetal reduction -- a procedure by which some of the multiples are killed off early in pregnancy -- has become common, it remains controversial.

Chang said the society's recommendation was a response to data published in the Journal of the American Medical Association Thursday that showed that doctors can now implant fewer embryos because they have a better idea than in the past which of the embryos will survive and grow.

But critics of the industry, while praising the move, characterized it as a response to growing alarm on the part of fertility patients who are frightened by the idea of going from zero to three children in a few seconds.

"It would be nice to think we now recognize the burdens and complications of multiple gestations, but I think it's largely due to the public outcry," says Dr. Kenneth Faber, a reproductive endocrinologist at a Kaiser-Permanente hospital in Denver. "If they could still get away with packing the uterus with embryos to have a marginally better pregnancy rate, they would -- but consumers increasingly are unwilling to tolerate an unsafe pregnancy."

"It's kind of like any other industry," Faber adds. Auto manufacturers "didn't make more fuel-efficient cars because [they] thought it was good for the environment. They did it because consumers realized it was a good idea."

In the past, Faber says, many of his patients tended to idealize multiple births. Now, "they go into chat lines and hear mothers who are ill and live chaotic lives full of financial ruin, and they don't want that."

The ASRM's recommendations are just that, recommendations, and the wording is loose. Partly that's because as long as the insurance industry doesn't pay for infertility treatment (it does in England and other European countries), women are frequently willing to gamble and get more embryos inserted in order to lower the chance that the implantation will fail. These would-be mothers know that if it does fail, they'll have to shell out another $6,000-$15,000 for another round of in vitro fertilization, or IVF, which is not only expensive but physically exhausting, involving the injection of numerous hormones.

Insurers don't want to cover infertility treatment because of its scale -- as many as 1 million people each year seek some kind of treatment. But the back-door costs to insurers, and the rest of us, are high. It can easily cost $500,000 just to keep a severely premature infant alive long enough to get out of the hospital.

Fertility specialists complain about the lack of insurance money for treatments, and also about the federal ban on embryo research, which they claim has slowed work on improving the process of growing and hatching embryos.

In most IVF procedures, doctors culture the embryo outside the womb for three days before re-implanting it. In recent years much excitement has been generated about techniques whereby doctors culture the embryo for an additional few days, after which they can have more confidence the embryo will thrive and become a baby. With that confidence, there would be less need to implant multiple embryos.

But the practice produces a peculiar byproduct -- a high rate of identical twins -- and when it fails, it can be difficult for the remaining embryos to be effectively frozen and saved for another cycle of IVF, says Dr. John David Gordon, co-director of Dominion Fertility and Endocrinology in Arlington, Va.

"We're striving for the day when you can put back a single embryo with the confidence it will become a baby," says Gordon. "It's a wonderful ideal but I'm not confident our patients will ever get that point."

So while fertility doctors tinker with new techniques, the chances are that high rates of multiple births will continue despite the ASRM's recommendations, which only cover IVF and not the more common and less controlled prescribing of fertility drugs.

"As a doctor you're sort of between Scylla and Charybdis. If you put three embryos back and they fail to impregnate there's a huge disappointment and Monday-morning quarterbacking," says Gordon. "But other times I'll put back three and get triplets. It's humbling. Sometimes Mother Nature does know best."