Watching the biological clock.

Physicians can predict when a woman will start menopause by giving her ovaries an ultrasound examination, according to a new study.

In an upcoming Human Reproduction, W. Hamish Wallace of the University of Edinburgh and Thomas W. Kelsey of the University of St. Andrews, both in Scotland, report that ovarian volume correlates with the number of primordial follicles, the sites in ovaries where immature eggs reside. An ultrasound test called transvaginal sonography, which can measure ovarian volume, therefore offers an easy, albeit indirect, way to gauge a woman's remaining cache of eggs, the researchers say.

As a woman ages, the number of these follicles declines. Menopause begins when she has about 1,000 eggs left. So, the researchers contend that when an ultrasound indicates a greater number of eggs, doctors could apply the established rates of egg-number decline to estimate a woman's remaining window of fertility.

"The accurate assessment of ovarian reserve will revolutionize the management of women requesting assisted conception, those who have bad treatment for childhood cancer, and those who are considering delaying a family for personal or professional reasons," Wallace and Kelsey conclude.