When a woman has regular menstrual periods, defined as regular cycles occurring every 21 to 35 days, this almost always indicates that she ovulates regularly. Ovulation of the egg occurs approximately 2 weeks before the start of the next period. If a woman has cycles at intervals of greater than 35 days, it may indicate that she is not ovulating an egg predictably, or even at all. Ovulation of the egg is essential for pregnancy. Therefore, we recommend an evaluation if menstrual cycles are infrequent or irregular in a couple attempting pregnancy.
