(ABC NEWS) -- A U.S. fertility clinic is luring patients from abroad with the promise of picking their baby's gender.
Each year, more than 200 women travel to The Fertility Institutes' New York and Los Angeles locations from countries where gender selection is banned, according to clinic director Dr. Jeffrey Steinberg.
"Women from countries like China and India tend to want boys. In the rest of the world, there's a slight preference for girls," said Steinberg, a reproductive endocrinologist, who trained in England where gender selection is illegal.
Using in vitro fertilization and preimplantation genetic diagnosis, or PGD -- a test designed to detect genetic abnormalities that cause disease -- Steinberg can select a baby's gender with 99.9 percent accuracy.
"There's tremendous pressure on some of these women," he said, describing how pressure to produce a boy under one-child policies can tear couples apart. "We're just happy to help them get it done."
The procedure is intense, starting with daily injections of fertility drugs in the women's home countries where "physicians can help them prepare for the procedure, they just can't do it," Steinberg said.
The drugs stimulate the ovaries to produce multiple eggs and prevent the woman from ovulating naturally, so that the process can be timed down to the hour.
"They take a shot to trigger ovulation, and then they have 35 hours to get here," said Steinberg, recalling how he once had to harvest eggs at 4 a.m. "You've got to time it just right, and we'll sometimes do 24 women in two days. It's a marathon."
The eggs are then fertilized with a partner's sperm in a laboratory and left to grow into embryos, from which a single cell is plucked and screened for the sex chromosomes. Embryos with the right chromosomal combo are then picked out and placed back in the woman's womb.
"Most couples are here for seven days," Steinberg said. "And for many of them, it's their first time in the U.S."
To coordinate care for women from all around the world, Steinberg staffs multilingual nurses and partners with a travel agent to arrange visas, hotels and transportation.
"They come here on very short notice and they need help planning their stay," said Sandy Flemming, president of World O' Travel in Woodland Hills, Calif. "We listen to their stories and try to be as comforting as we can; try to make them feel good about coming here."
Flemming said she has even lined up Disneyland tickets for patients' families in California.
"If they can be relaxed about all the arrangements, hopefully the procedure will more successful," she said.
Although gender selection is legal in the United States, some experts think it's unethical.
Dr. Mark Hughes, a pioneer in PGD technology, told "Good Morning America" he went into medicine "to diagnose and treat and hopefully cure disease. And last time I checked, your gender wasn't a disease."
"It's just raw sexism," said Art Caplan, a medical bioethicist at NYU Langone Medical Center, explaining how gender selection "crosses the line" from treating infertility to making designer babies.
"Are we going to outlaw it? No. But should clinics try to discourage it? Yes. If we don't discourage it, what's going to happen when someone says, 'I want a tall blonde?'"
The gender-selection procedure is also expensive, running upwards up $20,000 out-of-pocket, the combined cost of PGD and IVF. And most of Steinberg's patients don't even need IVF to get pregnant, he said.
But for some couples, the cost and criticism are no match for the guarantee of having a boy or a girl.
"It's a huge happy thing," Steinberg said, describing the wall of thank-you cards and baby photos in his clinic. "Of course, any pregnancy is a huge happy thing. But some women out there are just obsessed with getting what they're after."
While the proportion of foreign patients at Steinberg's clinic is increasing, most of his business still comes from U.S. couples.
Kristen and John Magill are one such couple. Seven years ago, they used PGD with hopes of rounding out their girl-heavy brood.
"We had three girls and really wanted to complete our family with a boy," said Kristen Magill, who in 2004 had three carefully selected male embryos implanted in her womb. "We wanted a boy to carry on the Magill name."
The couple from Fallmouth, Mass., ended up having twin boys: John Magill the 3rd and Patrick.
"I know there are people who don't believe it should be done, but I don't really have an opinion," Kristen Magill said. "We did it for our own reasons."