Claire Evans decided to freeze her eggs six years ago, when she was 36. She had just broken up with her fiancé and was worried that her time to have a baby was running out. A friend, whose own marriage had just ended, suggested the procedure.
She took medications to stimulate her ovaries to overproduce eggs, which were frozen to use later and to have a baby at an age when it would be difficult to become pregnant without medical intervention.
The procedure of egg-freezing is an increasingly popular, but expensive, option for women who want to delay childbirth. But new research documents some caveats: how old a woman is when she freezes her eggs and how many eggs she freezes make a significant difference in whether she will have a baby. Most women who tried to become pregnant, the study found, did not succeed, often because they had waited until they were too old to freeze eggs and had not frozen enough of them.
That note of caution comes from data published this summer in a paper in the journal Fertility and Sterility from the clinic where Ms. Evans froze her eggs — New York University Langone Fertility Center.
Dr. Marcelle Cedars, professor and director of the division of reproductive endocrinology at the University of California San Francisco who was not involved in the study, said that although it involved just a single fertility clinic, “it is a center that is unique for its long duration of follow-up.”
The data, she said, “are sobering” and “should give women pause.” Dr. Cedars, who is also the president of the American Society for Reproductive Medicine, or A.S.R.M., added that many women “are overly optimistic” about their chances of having a baby when they freeze their eggs. It is not, as many assume, an insurance policy.
“The pregnancy rate is not as good as I think a lot of women think it will be,” she said. “I always tell patients, ‘There’s not a baby in the freezer. There’s a chance to get pregnant.’”
The study, led by Dr. Sarah Druckenmiller Cascante, a fellow at N.Y.U. Langone, and Dr. James Grifo, director of the fertility center, reported that the average age when women froze eggs was 38.3. On average, they waited four years to thaw and fertilize their eggs.
The overall chance of a live birth from the frozen eggs was 39 percent. But among women who were younger than 38 when they froze their eggs, the live birthrate was 51 percent. It rose to 70 percent if women younger than 38 also thawed 20 or more eggs.
The age of the woman when she used the eggs to try to have a baby did not make a difference — all that mattered was how old a woman was when she froze her eggs and how many she froze.
“The reality is most eggs don’t make good embryos,” Dr. Grifo said. “The more eggs you have, the better the chance.”
According to the Society for Assisted Reproductive Technology, the number of healthy women freezing eggs rose to 12,438 in 2020 from 7,193 in 2016. But national data on success rates are pretty much nonexistent, said Dr. Timothy Hickman, president of the society and medical director of CCRM Fertility in Houston.
“I commend them for doing the study,” Dr. Hickman said of the N.Y.U. team.
Dr. Alan Penzias, a fertility specialist at Boston IVF Fertility Clinic and Beth Israel Deaconess Medical Center who is chair of the practice committee of the American Society for Reproductive Medicine said data from his center are consistent with the N.Y.U. study. At his center, he said, women who froze their eggs had just one-third of a chance of having a baby when they thawed them.
“Counseling should be clear that there is no guarantee and that the value of delaying having a child must exceed the benefit of delay,” Dr. Penzias said.
That trade-off is an issue with his 29-year-old daughter, Rebecca, Dr. Penzias said. Ms. Penzias — who gave him permission to mention her situation and use her name — wants to freeze her eggs because she is studying for a Ph.D. and is not ready to have a baby. Having some eggs frozen would give her peace of mind.
Dr. Penzias told her she does not need to freeze her eggs — she has plenty of years of fertility ahead of her — but he considers her reason for freezing sufficient.
His wife, a bioethicist and Ms. Penzias’s stepmother, disagrees, and said she should finish her degree, then try to get pregnant without frozen eggs.
Ms. Penzias decided to freeze her eggs, planning to do so in October.
Before choosing to freeze their eggs, women also must be prepared for substantial costs. Each egg retrieval cycle can cost $10,000, Dr. Hickman said. The number of eggs collected varies from woman to woman, and, for many, the only way to get a sufficient number to make success likely is to have more than one cycle.
It costs another $5,000 to $7,000 to thaw and fertilize the eggs, grow embryos in the lab for a few days, then implant them in the woman’s uterus. Many women, including Ms. Evans, have the embryos tested for chromosomal anomalies. That costs another $3,000. And storage of frozen eggs can cost up to $1,000 a year.
Some companies’ health insurance policies cover at least part of the costs. But many do not.
Most women end up never using their frozen eggs after paying for egg retrieval and storage, often because they got pregnant on their own.
Ms. Evans, though, is a success story. She was young enough when she froze eggs to have a good chance of success and to be able to have eggs retrieved twice to accumulate 20 that could be frozen.
She married in 2019 — to the same man she had been engaged to. Last year, she had her eggs thawed and fertilized in a laboratory with her husband’s sperm. Seven months ago, she had a baby girl, Fiona.
But the frozen eggs did not work for Ms. Evans’s friend who encouraged her to undergo the procedure. In 2020, she had the 10 or so eggs she’d frozen thawed and fertilized.
None developed into viable embryos.