Med center studies human egg-freezing techniques

Volunteers sought to test the viability of IVF procedure

Laboratories conducting in vitro fertilization have been freezing fertilized eggs for the last two decades, but freezing unfertilized eggs remains relatively new.

At Stanford, the in vitro fertilization laboratory freezes eggs on an experimental basis, usually for women who are about to undergo chemotherapy or radiation treatment and are concerned about losing their future fertility.

The IVF lab has now launched a study aimed at increasing the proportion of eggs that survive the freezing process and can be successfully fertilized (about 75 percent).

“We think egg freezing holds great promise, and this study will help us improve the technique and allow us to give patients better information,” said Lynn Westphal, MD, assistant professor of obstetrics and gynecology who is supervising the research.

Westphal has seen increasing interest in freezing eggs from women who wish to preserve their “younger eggs,” she said. A woman’s eggs have an increasing chance of chromosomal abnormalities after she reaches 35.

Her team will test whether trehalose, a sugar found in high amounts in Arctic fish and amphibians, can protect eggs against the freeze-thaw process. They also plan to test whether changing the salts in the solution in which the eggs are frozen or accelerating the freezing can improve egg survival.

The study will recruit volunteers from women who are already undergoing infertility treatment and have decided on IVF. The series of hormone injections to stimulate egg production and egg retrieval will not differ from the usual preparation for IVF. “The treatment is exactly the same,” said Westphal. “It would seem like the normal treatment cycle except that some of the eggs get frozen.”

The cycle of hormone injections takes six to seven weeks. The woman must take birth control pills to suppress her normal menstrual cycle and before her ovaries are stimulated to produce extra eggs.

During retrieval, doctors remove eggs from the ovaries with a small needle while the woman is sedated during a 15-minute outpatient procedure.

If the Stanford doctors have enough eggs (more than 10) after the retrieval procedure, they will set aside a few for freezing and thawing. Both frozen and unfrozen eggs will be fertilized by injecting sperm directly into the egg. Direct injection is necessary because freezing damages the zona pellucida, or the outer shell of the egg, to which the sperm needs to stick before penetrating the egg.

The discovery in the mid-1990s that sperm injection works well in fertilizing frozen eggs enabled doctors to begin experimenting with frozen eggs for IVF and transferring the resulting embryos back into the donors. In preliminary studies in Italy and Florida of pregnancies after egg freezing, doctors have not found an increased rate of birth defects once the embryos develop.

However, only a few hundred babies have been born from frozen eggs, said Barry Behr, PhD, assistant professor of obstetrics and gynecology and director of the IVF lab. He said the procedure should still be considered experimental until doctors collect more data.

The Stanford team will monitor the frozen and unfrozen fertilized embryos outside the womb up to day six of development before deciding which ones will be transferred back into the egg’s donor. “We will transfer the best embryos, irrespective of whether they come from frozen or unfrozen eggs,” said Behr. “That gives the best chance for the woman to have a healthy pregnancy.”

Women participating will have a reduction in the cost of IVF because Serono, a pharmaceutical company that makes the hormones doctors use to stimulate egg production, is sponsoring the study. The average cost of the IVF procedure is around $12,000. Westphal estimates that women participating in the study could save between $3,000 and $4,000 in medication expenses.

Study participants must be younger than 36. Those interested in volunteering should call Westphal at 498-7911.