Indirect evidence of the occurrence of ovulation, which is generally accepted, is an increase in plasma or serum progesterone. Pelvic ultrasonography can estimate the probable time of ovulation within 12 h. There is a close association between the rise in progesterone, luteinizing hormone (LH) and oestrogen peaks and ovulation. A WHO study reported that ovulation occurred at a median time of 8 h after the rise in plasma progesterone, 15 h after the LH peak and 24 h after the oestrogen peak. The basal body temperature (BBT) method is the most effective in determining the premenstrual infertile period, but it is unreliable for an accurate determination of ovulation and the postmenstrual infertile period. Nor is BBT an effective method of predicting ovulation during postpartum lactational amenorrhoea. Therefore, BBT is usually used as a secondary indicator of ovulation and is combined with more reliable indicators. Observed changes in cervical mucus patterns can be used to define the probable fertile period, although this method produces a wide range of days. The peak mucus symptom is closely correlated with ovulation. Mucus symptoms can be used as a guide for the timing of blood or urine samples for estimation of LH, oestrogen and progesterone or their metabolites. Symptothermal methods incorporate other symptoms such as cervical changes, intermenstrual pain, breast tenderness and backaches, but these are secondary signs of ovulation and are recommended to be used in conjunction with mucus and BBT.
PIP: Natural family planning (NFP) methods are based on the observation over the course of the menstrual cycle of specific signs and symptoms that result from changes in circulating blood levels of ovarian steroids, estrogen, and progesterone. There is a close association between the rise in progesterone, luteinizing hormone (LH), and estrogen peaks and ovulation. The basal body temperature (BBT) method is often incorporated in NFP methods that use 2 or more signs and symptoms of ovulation and is a simple, inexpensive way to determine the premenstrual infertile period. However, this method is not accurate in estimation of the day of ovulation, the postmenstrual infertile period, or the prediction of ovulation during postpartum lactational amenorrhea. The observation of changes in cervical mucus patterns can be used to define the probable fertile period of the menstrual cycle, but produces a wide range of days. The peak mucus symptom further can be used as a guide for the timing of blood or urine samples for the estimation of LH, estrogen, or progesterone. Changes in the morphology of the cervix, intermenstrual pain, vaginal bleeding, breast tenderness, vulval swelling, and backache have been incorporated into symptothermal NFP methods as secondary indicators of ovulation and can be used in conjunction with BBT and mucus observation. Under development are a number of electronic devices that will increase the ability to accurately determine the fertile and infertile phases of the menstrual cycle. A critical future need is more research on the reliability of NFP methods in breastfeeding women and the possibility that an increase in the volume of mucus may be a marker of the return of ovulation in lactating women.