ESHRE: Fast Freezing of Eggs Seen as Fertility Option

PRAGUE, Czech Republic, June 21 ? Rapid cryopreservation of human eggs may have a future in substantially extending the practical time limits on women's fertility, according to early Japanese clinical research reported here.

With the new method, nearly 95% of the fast-frozen eggs survived, and the pregnancy rate using these eggs was nearly 42%, the same rate as for fresh eggs, said Masashige Kuwayama, Ph.D., of the Kato Ladies Clinic in Tokyo reported at the European Society of Human Reproduction and Embryology meeting here.

As opposed to conventional "slow freezing" of human oocytes, Dr. Kuwayama's method involved rapid freezing in a small amount (less than 0.1 mcL) of vitrification solution. The process prevents ice crystals, which damage the egg's structure, from forming, Dr. Kuwayama and colleagues said.

The method may prove especially useful for women who can not or do not want to freeze embryos for possible use in the future, the Japanese scientists said.

The Japanese researchers reported the following clinical outcomes with 111 eggs from women ages 25 to 37 frozen by the new "minimum volume cooling" method:

• 94.5% of the eggs survived the freezing and thawing.
• 90.5% were successfully fertilized.
• 50% of the resulting zygotes were successfully developed for embryo transfer.
• Twelve pregnancies resulted from 29 embryo transfer procedures (a nearly 42% success rate), with an average of 2.3 embryos transferred per procedure.
• Eleven healthy babies were born (nine singletons and one pair of twins). Two pregnancies miscarried.

"The conventional slow freeze-thawing method has been used successfully for human embryos in assisted reproduction for two decades, but has been far less successful for oocytes," Dr. Kuwayama said.

"This technology opens up new horizons for medically assisted reproduction in women, enabling them to have the option of having children at a later date by freezing eggs rather than embryos," Dr. Kuwayama said. "Moreover, it will help to eliminate the existing time differences in fertility between men and women, whereby women's supplies of eggs decline at a faster rate than men's supplies of sperm."

In another presentation at the meeting, an Italian group appeared to confirm that conventional slow freezing of human eggs is less successful than the rapid freezing method.

Sandrine Chamayou, Ph.D., of the Unita de Medicina Della Riproduzione in Catania, Italy, reported the following outcomes with 337 eggs frozen with the conventional method:

• 78% survived the freezing and thawing.
• Nearly 68% were successfully fertilized.
• Two pregnancies resulted from 37 embryo transfer procedures, with an average of 2.5 embryos transferred per procedure.
• Two babies were born.

The slow-freezing method does not offer "stable results to guarantee high clinical expectations," Dr. Chamayou concluded. "But in Italy where embryo freezing and surplus embryo production are forbidden, oocyte cryopreservation is a possibility to maximize the chances of reaching a pregnancy with a single ovarian stimulation."