Ovulation Prediction: Why, When and How

Knowing when ovulation occurs is important not only with regard to the treatment of infertility and reproductive failure, but also with regard to planning a family. The ability to do this allows for scheduling or avoiding intercourse around the "fertile period" (immediately prior to ovulation occurring). Since in about 25% of cases infertility is attributable to absent or dysfunctional ovulation, it is important to be able to accurately confirm that ovulation occurs at the right time and that this is followed by normal hormonal activity of the corpus luteum (the ovarian unit that produces progesterone and estrogen post-ovulation).

The menstrual cycle can be divided into two parts. The first part, (the proliferative or follicular phase) comprises the time preceding ovulation when the ovarian follicle(s) produce(s) estrogen that causes the endometrial lining to proliferate (thicken). The second part (the luteal or secretory phase) commences with ovulation and ends with the onset of menstruation.

During the secretory phase, the ovarian corpus luteum produces both estrogen and progesterone, and the glands of the uterine lining (the endometrium) become filled with secretions intended to nurture the early root system of the implanting embryo. The proliferative phase can vary in length, while the normal secretory phase is usually constant in duration (+/-14 days). A secretory phase of less than 10 days is suggestive of an underlying ovulation dysfunction (a luteal phase defect), which usually requires treatment.

The occurrence of "premenstrual molimena" (breast engorgement, some bloating and mood changes), a progesterone effect, followed by regular cyclical menstrual bleeding associated with some cramping during the first 36 hrs suggests that the woman likely is ovulating.

Knowing the timing of ovulation is important because a woman only ovulates once a month and the ovulated egg can only survive for about 24 hours. In most women, ovulation occurs about 14 days prior to the onset of bleeding, which, in a normal menstrual cycle of 28 days, would be day on day 14. However, since the length of the cycle varies depending of the length of the first half, ovulation does not always occur on the same day.

An inexpensive method for pinpointing the day of ovulation is for the woman to record her basal body temperature (BBT) each morning prior to drinking any liquids or brushing your teeth. In the first half of the cycle the normal basal temperature is around 98° F. Twelve (12) to 24 hours following ovulation the temperature rises by just less than a degree. Charting the BBT is a good way to document ovulation, and allows measurement of the length of time from ovulation to menstruation (i.e., the luteal phase), but is less helpful when it comes to pinpointing the” fertile period” (by which to time intercourse). This is because the body temperature rise only occurs after ovulation has already occurred, by which time, the cervical mucus will already have changed in consistency, and act as a barrier to sperm entering the cervical canal en route to the egg in the Fallopian tube.

When it comes to pinpointing the “fertile period” so as to time for intercourse, ovulation predictor kits (OPK) are more helpful than measurement of BBT. They can be purchased at most drug stores and supermarkets. The OPK measures luteinizing hormone (LH) in the urine. Since it is the spontaneous LH surge that triggers ovulation, this can be reliably predicted to occur within 6-36 hours of the urine OPK testing positive. It is also possible to document ovulation by performing a series of sequential daily pelvic ultrasound exams around the anticipated time of ovulation.

The detection of a significant blood concentration of progesterone in the second half of the menstrual cycle is also suggestive of ovulation having occurred. Irregular or delayed menstrual cycles suggest dysfunctional or absent ovulation. Increased blood levels of the hormone prolactin or an imbalance of the normal estrogen-progesterone ratio in the secretory phase of the menstrual cycle are likewise often associated with absent or dysfunctional ovulation. Increased ovarian production of male hormones such as testosterone an/or androstenedione often occurring a condition called polycystic ovarian syndrome (PCOS), which is one of the commonest causes of absent or dysfunctional ovulation in women of the reproductive age.

In conclusion, it is important to recognize that aside from a pregnancy, no single test or examination provides absolute confirmation of ovulation.