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Most women experienced either two or three "waves" of ovarian activity during one menstrual cycle. Eggs developed to a mature or nearly mature size, and then most dissolved. Only one wave of follicular (egg follicle) development resulted in ovulation, as a result of the surge in luteinizing hormone. Consistent with current knowledge, the egg that successfully ovulated was developed during the first half of the menstrual cycle (the approximately two-week period beginning with menstruation). The nonovulatory waves happened after ovulation (the approximately two-week period before ovulation).

What the study might change—and what it won't
If confirmed by additional studies, this research has potential to improve women's health, especially in the area of infertility. Some women undergoing infertility treatment use medications to stimulate the development of eggs. Sometimes those eggs are harvested for in vitro fertilization, that is, they are removed from the woman's body and inseminated, and then placed back in the body. Other assisted reproductive technologies stimulate egg development without egg harvesting. These treatments have been extremely time-sensitive, because scientists believed that there was only one opportunity per cycle to stimulate eggs. This research indicates that infertility treatments may use eggs produced during the second half of the cycle, resulting in a great increase in the number of eggs available for infertility interventions. This could significantly reduce the time couples spend pursuing infertility treatments.

These findings may also carry implications for birth control methods that intervene in the ovulation process (hormonal methods such as the pill or patch, injections, implants, and hormone-releasing IUDs).

Media reports that say this study confirms the ineffectiveness of natural birth control are false. Because, in their mistaken view, women ovulate numerous times per month, it is then impossible for women to identify their fertile times. However, women do not ovulate more than once per menstrual cycle (except on the rare occasions when two eggs are released at the same time, which may result in twins). Each ovulation is associated with growth of the uterine lining, which must either result in a pregnancy or be shed in menstruation before another ovulation may occur. The ovulatory wave of follicular activity is associated with changes in a woman's temperature, cervical fluid, and cervix position, all of which may be charted with great accuracy. This is because when an egg is preparing to ovulate, several other hormones are at work producing these physical changes. The nonovulatory waves of follicular activity are not noticed by natural family planning methods. In the second half of a woman's cycle, different hormones are at work, and these do not produce fertile symptoms.

This new ovulation study carries more immediate implications for infertility and for hormonal birth control than for natural birth control. Natural birth control was developed in the mid-20th century by two Roman Catholic scientists who wondered why the rhythm method was so ineffective. The rhythm method involves counting days on a calendar, assuming fertility in the middle of a cycle. Contemporary methods use daily knowledge of the body's symptoms of fertility—with no assumptions based on cycle length. Attention to cervical fluid and temperature is a scientific approach that has entirely replaced the rhythm method, with wonderful increases in effectiveness.

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July (Web-only) 2003, Vol. 47