She had the name picked out since high school: Logann Rae, taken from a soap opera. She had two dolls waiting in a closet, both saved since childhood. Tanya had always dreamed of having a daughter, and of the intimate bond that would grow as they picked out dresses together, styled their hair and painted their fingernails. But Tanya's first child was a son. Then came another. When an ultrasound showed that her third child was also a boy, she struggled to hide her tears from the nurse.

And that is why this year she drove 400 miles to a doctor's office in Westwood. Using methods common in fertility clinics, doctors mixed Tanya's eggs with her husband's sperm to create five embryos in a laboratory dish. Then, using a new technique, they examined the embryos to determine which had the DNA to become boys, and which were programmed to be girls.

The three male embryos were frozen, their fate to be decided later. The two female embryos were transferred to Tanya's womb in an attempt to create the daughter she always wanted. The embryo-sorting technique--called PGD, for pre-implantation genetic diagnosis--is quickly becoming the most controversial development in high-tech reproduction. Doctors are able to screen embryos not only for gender, but for whether they carry the genes involved in cystic fibrosis, sickle cell anemia and more than 100 other inherited diseases. They can even tell whether an embryo would grow into a good cell donor to help a sick person. The information is helping parents choose which embryos they want--and which to reject as unhealthy, or merely undesirable. The cost is about $10,000, including the price of in vitro fertilization, the procedure that creates "test-tube babies" and which is a required part of embryo screening.

But as the number of doctors offering the service leaps upward, embryo screening is raising some profound questions: Is it proper to discard an embryo based on its genes or gender? Which lives are not worth living? Who decides?

"It's scary to have this power," said Tracy Otte of Fountain Valley, who is trying to have a child and avoid the muscular dystrophy that killed two brothers in their early 20s. "If this technology was there, would my brothers ever have been born? It becomes: Did their lives have value? Absolutely, they had value. But it was also tragic to see how young they died."

Some fertility specialists say the questions will only become thornier, as scientists are bound to create tests not only for disease but for various traits. "There will come a day when we can determine height or weight or skin tone characteristics, and the question is: What do we do with that information?" said Dr. Jeffrey Steinberg of the Fertility Institutes in Tarzana, which has offered embryo screening for about a year. Society at large "has to give us feedback, because this is as new to us as it is to the rest of the world."

"We've arrived at the point where we need a national debate--no doubt about that," said David Hill, scientific director at ART Reproductive Center of Beverly Hills, which offers embryo screening services.

It is far from clear if parents will ever be able to test for intelligence or athletic ability, which are presumed to involve many genes and environmental factors. Still, embryo screening is one of several developments that could give parents significant control of their children's genetic makeup.

Armed with data from the Human Genome Project, researchers are probing the genetic foundations of obesity, mood and disease. Testing devices called "gene chips" are allowing scientists to track the activity not of one gene, but of thousands at the same time. Cloning and genetic engineering have enabled biologists to augment the genetic makeup of animals, adding genes so that the animals grow faster, bigger or more resistant to disease.

But even before scientists gain additional powers over human reproduction, there is worldwide debate over how to handle the information embryo screening can reveal.

Debate Began in Late '80s

The debate has been building since the late 1980s, when doctors at London's Hammersmith Hospital learned how to tease a cell from a 3-day-old embryo and study its chromosomes for gender. By weeding out male embryos from the females, the doctors aimed to help parents avoid such gender-linked diseases as hemophilia and Duchenne muscular dystrophy, which are inherited overwhelmingly by boys.

Later techniques allowed doctors to screen for the genes that cause a variety of diseases. The screening, however, has become widely available only in the last two years, as more companies have begun handling the sophisticated laboratory work for fertility doctors.

While no one keeps complete numbers, specialists say about 50 U.S. clinics now offer the service to patients. Nearly 2,000 embryo-screened babies have been born worldwide since 1992.

Embryo screening has caught the attention of Joy Pablo, 34, a Los Angeles nurse who has battled breast cancer since 1998. She worries that her 5-year-old daughter will one day face the disease. She hopes her next child can escape the same fear.

"If they could guarantee me a boy, I would have peace of mind," said Pablo, "because the chances of breast cancer are so much smaller than with a girl."

For Otte, 37, whose brothers died from muscular dystrophy, the idea of rejecting a potential child because of the disease is unsettling.

Her brothers had friends and went to college--one went to his high school prom. "They had this disease, but they weren't this disease," she said. Nonetheless, she is trying to have a daughter through embryo screening because muscular dystrophy rarely strikes girls.

"I know the road map of this disease, and it's too tough to repeat that," said Otte, a third-grade teacher. "At age 8 or 9 you start thinking about a wheelchair. A cold can kill because there's no strength to cough up mucus."

When having children, people such as Pablo and Otte often roll the genetic dice and hope for the best. Or they become pregnant and use a prenatal test, such as amniocentesis, followed by an abortion if the test turns up a problem.

With embryo sorting, "they can start their pregnancy on Day One with a commitment to continuing it," said Dr. Mark Hughes of Wayne State University in Detroit, who helped develop embryo diagnosis with the Hammersmith doctors. "How can it be more ethically troublesome to test before a pregnancy than later, when the fetus has a heartbeat and is moving?"

Many Ethical Concerns

And yet, something about embryo screening makes many people nervous, even people who do not see the embryo as equivalent to a child.

Where amniocentesis usually provides information about a single fetus, embryo screening allows parents to judge and reject many potential children at once. And because it bypasses the pain of abortion, some fear it will be used too freely, coarsening attitudes toward the embryo.

In Germany, the federal government has barred embryo screening for any purpose. In England, it can be used to select a child's gender only when there is a medical need.

But in the United States, fertility techniques are regulated more lightly, and there are no restrictions on how embryo screening may be used. That leaves policy to be set by people such as Dr. Jaroslav Marik of the Tyler Medical Clinic, the doctor Tanya visited in her attempt to conceive a daughter.

A regal man of 69, Marik has worked at the Tyler clinic, in the shadow of the UCLA campus, since 1971. He was one of the first doctors in a Western state to offer in vitro fertilization. An enthusiastic defender of patient choice, Marik believes embryo screening has the potential to nearly eliminate diseases such as cystic fibrosis.

But he also does not shy from offering it to patients who have no medical need to select a child's gender. "What is medical need?" he asked. "Isn't the right to happiness and health a part of that?"

"Is there a medical reason for Dolly Parton to have boobs like that?" he asked. "Is there a medical reason to have liposuction? Is that a misuse of medical technology?"

Marik, who works with embryologist Jerry L. Hall, said about 70 of his patients have screened embryos since 2001, including 15 who sought a boy or girl for non-medical purposes.

He believes he does the screening with proper respect for the embryo. Patients work hard to make embryos and want some good to come from them, he said. They usually ask that rejected embryos be donated to research or, when they are healthy, to infertile couples.

"I hardly remember anyone who instructed us to destroy the embryo," he said.

But much of Marik's reasoning raises concerns among critics of embryo screening--a constellation that includes antiabortion groups, feminists, advocates for the disabled and people within the fertility profession.

Flaws, Embryo Rejection

Rejecting a boy or girl when there is no medical need draws the most objections.

"Morally reprehensible," said Dr. Robert E. Anderson of the Southern California Center for Reproductive Medicine in Newport Beach. "Most Americans, no matter where they come down on the question of where life begins, would find something morally objectionable about creating embryos and then discarding some simply because of their sex."

"It is inherently sexist. It values one sex in favor of another," said Tania Simoncelli of the Center for Genetics and Society, an Oakland public policy group.

Hughes, the Wayne State doctor, said: "I went into this to help people with disease. Last time I checked, your gender is not a disease."

Some also argue that allowing gender selection endorses lopsided gender preferences in other countries. In some parts of India, where boys are heavily favored for economic and other reasons, there are only 86 women for every 100 men. Parents commonly use sonograms and abortion to avoid having girls, though the practice is illegal.

Still, some Indian fertility doctors bridle at the notion of being bound by Western views. "I do not understand why some Indians are ashamed that most Indians want to have boys," said Dr. Aniruddha Malpani, who has produced 22 children--all boys--from screened embryos at his Bombay clinic. "The preference for sons is based on traditions which are centuries old, and these preferences are not going to change quickly."

Using embryo screening to detect disease has also drawn protest.

Embryo tests can detect the genes behind cystic fibrosis, for example, but not whether the illness will be so mild that symptoms are negligible, as sometimes happens. Some critics say it is immoral to reject a potential life on the basis of a disease that may turn out to be mild.

Some people argue against rejecting even embryos destined to have severe disease. "Most people with disabilities rate their quality of life as much higher than other people think," said Deborah Kaplan, executive director of the World Institute on Disability in Oakland. "People make the decision [to reject embryos] based on a prejudice that having a disability means having a low quality of life."

There is a subjective component to deciding whether any disease or flaw is severe enough to make life not worth living. When Dorothy Wertz of the University of Massachusetts Medical School surveyed U.S. genetics professionals in 1995, she found that about 30% would abort a pregnancy if the child was destined to have severe obesity--something she considers to be more a cosmetic condition than a disease.

The biggest use of embryo screening could have nothing to do with disease in the traditional sense. Instead, screening may become a routine way to boost the success of in vitro fertilization.

Embryos that look fine under the microscope often self-destruct in the womb because of extra or missing chromosomes. Some doctors are now screening for these faulty chromosomes before choosing which embryos to transfer to patients.

"The embryologists who begin to work with this, their jaws just drop as they look back and say, 'Hey, how many of these embryos that looked perfect but were doomed to failure have I loaded into a catheter and transferred to a woman?' " said Dr. Beth Ary of the Reproductive Specialty Center in Newport Beach.

But this use of embryo screening is controversial as well. Some doctors note that clinics test no more than eight of the 23 pairs of chromosomes, and problems could be hiding in the others. They also worry that embryos are damaged in the process of pulling off a cell.

But Ary and her embryologist husband, Jim, said the birth rates at their clinic rose after they began offering embryo screening to patients in March 2001. And a Spanish study found screening raised pregnancy rates among women who had repeatedly lost pregnancies for unexplained reasons.

Hoping for a Little Girl

For Tanya, the visit to Marik's office was a final effort for a daughter. After three boys, her husband was willing to have only one more child.

"They say the odds are 50-50 of having a girl," she said earlier this year. "But it isn't for me, anyway."

She was dressed in a bathrobe, lying on a gurney in a Tyler clinic examination room. Two female embryos had just been placed inside her. She had asked Marik to give researchers the three male embryos she created, or to donate them to an infertile couple, at his discretion.

Tanya said she is comfortable using the technology but fears some relatives, who are devout Roman Catholics, would object if they knew. She asked that her last name and hometown not be printed.

She talked about her love for her sons, but also about a longing to re-create the intimacy that she enjoys with her own mother. "It just seems that when boys get older they close up a little more and get married, and the wife takes on that closeness," she said.

While her husband bonds with their boys through fishing and golf, Tanya dreams of barrettes and nail polish. "I do my boys' hair up," she said. "I put in lots of gel and spike it up real fancy. I painted their toes, but my husband said, 'I don't think we're going to start that.'

"He said: 'You need a girl.' "

Two weeks after her visit came the news she had wanted for so long: She was pregnant. "There was so much desire, and now it's being fulfilled," she said.