Cervical Mucus During the fertile window, cervical secretions at the vaginal introitus are slippery and clear, while secretions at other times of the menstrual cycle are dry and sticky (32,130). The volume of cervical mucus peaks 2 to 3 days prior to ovulation, thus identifying higher day-specific probabilities of conception (32).
Luteinizing Hormone Monitoring At a mean time of 2 hours following the peak of the serum LH surge, urinary LH can be detected. Commercially available kits for documenting the LH surge are generally accurate, quick, convenient, and relatively inexpensive enzyme-linked immunosorbent assays (ELISA) that use 35 to 50 mIU/mL as their threshold for detection (132,133). Once the LH surge is detected, ovulation may occur within the next 48 hours (32,132,133). The positive-predictive and negative-predictive values for these kits have been described to be 92% and 95%, respectively (132,134). Because the duration of the surge may be less than 12 hours, twice daily testing may increase detection rates (133). However, the 2 days of highest probability of conception are the day of and the day prior to the LH surge, so this may actually lead to abstaining from intercourse during a potentially fertile time (127). False-positive rates occur in 7% of cycles, which may reﬂect urinary clearance of unsustained premature LH surges (32,131,135). The tests cannot be used in patients with irregular cycles (127).
Midluteal Serum Progesterone When used to document ovulation, serum progesterone measurement should coincide with peak progesterone secretion in the midluteal phase (typically on days 21 to 23 of an ideal 28-day cycle or 7 days following the LH surge). The lower limit of progesterone levels in the luteal phase varies among laboratories, but a level above 3 ng/mL (10 nmol/L) typically confirms ovulation. However, interpretation of isolated luteal-phase measurements of serum progesterone is complicated by the frequent pulses that characterize the secretion of this hormone. Although ovulatory levels are often considerably higher than 3 ng/mL, low midluteal serum levels of progesterone are not necessarily diagnostic of anovulation (124).
Ultrasound Monitoring Ovulation is characterized both by a decrease in the size of a monitored ovarian follicle and by the appearance of ﬂuid in the cul-de-sac using transvaginal ultrasound (124). Follicles reach a preovulatory diameter of 17 to 19 mm in spontaneous cycles or 19 to 25 mm for clomiphene-induced cycles (136,137). A combination of LH testing and ultrasound can be used, with LH kit testing starting when the ultrasound-measured follicle size reaches 14 mm (131). Ten percent of the cycles of normally fertile women may have a luteinized unruptured follicle, whereby progesterone is released and the luteal phase progresses normally without visible signs of follicle rupture when daily ultrasounds are performed from cycle days 10 to 20. This incidence is increased to 25% in women with unexplained infertility (138). Because of the inconvenience and expense of serial measurements, ultrasound monitoring should be reserved for patients who fail less expensive methods for detecting ovulation or for certain types of ovulation induction (124).
Follow-Up Tests In women with absent or infrequent ovulation, serum FSH, prolactin, and thyroid-stimulating hormone (TSH) testing should be performed (124).