In a typical reproductive cycle, a single follicle (containing a single egg) reaches maturity after 2 weeks, culminating with the release of that egg in a process called ovulation. Once ovulation has occurred, a menstrual period will occur 12-14 days later unless pregnancy supervenes. Thus, most women cycle every 28 days (14 days to grow the egg and 14 days after ovulation until period returns).
Understandably, if a woman has irregular and unpredictable cycles, then logic suggests that she is probably not ovulating normally. Ovulatory problems are usually divided into two main categories: problems with the ovary and problems with the signals from the brain to the ovary. If the irregular cycles result from a lack of follicles within her ovary, then the failure of the ovary to respond will cause the pituitary gland to secrete increased amounts of follicle-stimulating hormone (FSH).Women with elevated levels of FSH are described as having diminished ovarian reserve; if their periods cease entirely, then they are described as having premature ovarian failure (POF). Laboratories may differ as to how they define an “elevated” level of FSH, so a discussion with your physician is crucial to correctly assess the results of this test. In most cases, however, an FSH level of more than 15 IU/L is evidence of diminished ovarian reserve; FSH levels exceeding 30 IU/L usually signify POF.
If a woman has a normal complement of follicles but still does not have normal cycles, then the problem must lie elsewhere. Most such women suffer from a communication mismatch between the brain and ovary, disrupting the carefully coordinated hormone signals that induce the growth of ovarian follicles. The causes of this disruption can be further classified, with most patients being found to have polycystic ovarian syndrome (see Question 23) as opposed to other hormonal imbalances.