Breastfeeding is a natural contraceptive against another pregnancy. The longer the mother nurses, the longer she delays the return of fertility. A natural mechanism triggered by breastfeeding interrupted Ms. El-Hady's monthly cycle of ovulation and menstruation. Depending on how long and how often she suckles her child, this infertility, termed lactational amenorrhea, could last as long as 2 years. This traditional method of spacing births offers protection against pregnancy to more women than all other methods of contraception combined, according to family planning researchers. With growing trends away from breastfeeding, the traditional practice is losing its impact on fertility. Not many women in Egypt use modern contraceptives. There is little understanding of lactational amenorrhea, but researchers are giving it more attention as they continue to search for effective family planning methods appropriate to the needs and circumstances of the rural population. They know that the effect is only temporary and varies from woman to woman. Ms. El-Hady has been amenorrheic for 15 months, but other women experience much shorter periods of amenorrhea, and some none at all. The secretion of milk is promoted by a hormone called prolactin that the anterior pituitary gland produces in large quantities during pregnancy. The frequency and duration of breastfeeding appear to determine the length of amenorrhea, although the mother's nutrition and any other type of contraceptive used may also play a role. Each month for 2 years, Dr. Olfat Darwish, professor of nutrition at the University of Alexandria's High Institute of Public Health, has visited 260 rural mothers and 290 urban mothers to gather data on diet, breastfeeding practices, state of amenorrhea, and use of contraception. The length of the breastfeeding period was found to affect the duration of amenorrhea. Early weaning brought an earlier return of ovulation and menstruation, and thus of fertility. The nutritional status of the mothers did not appear to affect the length of the period of amenorrhea. An understanding of how the mechanism operates and what its limitations are will enable family planners to offer women an additional contraceptive choice.