TRANSFERS BY AGE Frozen embryos are used in fewer than 20% of in vitro fertilization attempts. In 2006, a total of 17,533 previously frozen embryos created from women's own eggs were transferred to their uterus. By age:   Number of transfers Percentage resulting in live births Under 35 9,114 33.1 35-37 4,814 28.0 38-40 2,729 22.9 41-42 876 20.7 Source: Society for Assisted Reproductive Technology  YOU CLICKED: WEEK'S MOST POPULAR HEALTH STORIES 1: Doctors ditch drug samples to avoid influencing treatment 2: Report: TV, Internet harm kids 3: Faces or finances? Economy cuts into cosmetic procedures 4: Recipes for creative, diet-friendly Thanksgiving leftovers 5: Galveston hospitals swamped by hurricane 6: Your Health: The end-of-life discussion can be made easier No. 7-10: Hospital havens, lasting love

In what they describe as the largest and only multi-center study of its kind in the USA, researchers surveyed patients with frozen embryos at nine fertility clinics. Only about two-thirds of the 1,020 respondents said they were likely to use their embryos.

But whether they reported wanting another baby or not, more than half of the respondents said they were "very unlikely" to donate extra embryos to another couple trying to have a baby. That finding contradicts the conventional wisdom, says lead author Anne Lyerly, a Duke University obstetrician/gynecologist and bioethics researcher.

"If you look at the policy debate and the discussion in the literature, there is a presumption that if you respect or care about an embryo, you would want it to become a child," Lyerly says. But, she says, patients apparently feel responsible for the care of the children resulting from their embryos.

The most popular option was donating the embryos for research, the survey found. Among patients who reported they didn't want a baby, four out of 10 said they'd be "very likely" to donate their leftover embryos for research. Among those who reported wanting a baby, 15% said they'd be "very likely" to donate leftover embryos for research.

The problem, Lyerly says, is that a ban on federal funds for research involving embryos prevents most fertility patients from choosing that option. Even without the ban, shipping them is tricky, she says. In addition, concern about proper informed consent procedures would make researchers reluctant to accept frozen embryos from other medical centers, says Sean Tipton, a spokesman for the American Society of Reproductive Medicine, whose journal, Fertility and Sterility, posted Lyerly's study.

Elizabeth Ginsburg, medical director of the IVF clinic at Boston's Brigham and Women's Hospital, says some patients have asked for their embryos. "I don't know what they do with them," she says.

Fewer than one in 10 said they were very likely to pick the other options, which included holding a ceremony while thawing and disposing of the embryos. One in seven said they were likely to freeze their embryos "forever." Clinics typically charge "a few hundred dollars" annually to store frozen embryos, Tipton says, adding that some clinics raise the price over time as an incentive for couples to get them out of storage.

The question of what to do with leftover embryos "absolutely should be raised at the beginning" of fertility treatments, Lyerly says. At the least, she says, the storage bill should mention it.