Egg glitch: too cold or old.

Egg glitch: Too cold or old

Although human in vitro fertilization has become routine, it produces pregnancy only 20 to 25 percent of the time. Researchers have now shown how three factors -- lab procedures, the implanted embryo and the uterine lining -- can influence the success rate. Moreover, one of their findings may offer menopausal women another chance at pregnancy.

Cryopreservation -- freezing embryos in storage -- significantly reduces the odds of successful implantation, scientists from Tel Aviv University conclude in the Oct. 25 NEW ENGLAND JOURNAL OF MEDICINE. In a study of 57 menopausal women, they found that those implanted with frozen donor embryos showed an overall pregnancy rate of only 15 percent, compared with 37 percent among those receiving fresh donor embryos. Lab manipulations for cryopreservation may impair the embryo's capacity to develop in the uterus, suggests coauthor Laslo Nebel. However, he would not discard cryopreservation altogether because it offers practical advantages and in some cases yields "quite good results," he told SCIENCE NEWS.

Another new study, described in the same journal, points to aging eggs and declining hormone levels--not the uterus itself -- as reasons for the age-related decline in the ability to become pregnant and bear a healthy infant. Mark V. Sauer and his colleagues at the University of Southern California in Los Angeles treated seven menopausal women, aged 40 to 44, with hormones that restored the uterine lining to its premenopausal state. Then they implanted fresh, fertilized eggs -- from donors aged 31 to 34. The result: four pregnancies that went to term. Nine women aged 27 to 39 underwent the same treatment with the same success rate, Sauer reports. Such results, he says, "dispute the idea that the uterus ages in a bad way."