Reproductive Medicine and Infertility Services
Follicular growth can be measured with ultrasound, a technique which uses sound waves to produce an image on a monitor screen. This is a painless procedure that can be done using either a vaginal probe or an abdominal scanning device. Prior to ovulation, the follicle is thin-walled and filled with fluid. As the egg inside the follicle develops, the follicle increases in size. Ovulation generally occurs when the follicle measures about 1.6 to 2.5 centimeters. Ultrasound is especially useful for timing intercourse or insemination. In women taking fertility drugs, ultrasound may be performed on several different days during the menstrual cycle so that each follicle can be carefully measured and monitored.
Ovulation Prediction Kits
Several ovulation prediction tests are available at drug stores. These kits use paper dip sticks that show changes in the level of LH in the urine. Once the LH surge has occurred, ovulation usually takes place within 12 to 44 hours. Urine testing usually begins two days prior to the expected day of ovulation. For women with 28-day cycles, ovulation usually occurs on days 13 to 15. For women with irregular menstrual cycles, urine testing should be timed according to the earliest and latest possible dates of ovulation. If the cycle ranges between 27 and 34 days, ovulation usually occurs between days 13 and 20. Therefore, testing should begin on day 11 and continue until ovulation is indicated or through day 20. There is an 80 percent chance of detecting ovulation with five days of testing and a 95 percent chance with ten days of testing. Once ovulation is documented, it is no longer necessary to continue testing. Occasionally, ovulation may not occur in a particular cycle. If ovulation is not detected in two or more consecutive cycles, an ovulatory problem may be present.
The following are general guidelines for ovulation prediction tests that are based on detecting LH in the urine:
- The manufacturer's instructions should be followed precisely.
- Urine that is very dilute (light) may not have an adequate concentration of LH for detection. Therefore, women should avoid food and liquids for two to four hours before obtaining urine for testing so as to have an adequately concentrated (dark) urine sample.
- False positive results in urinary LH detection may occur if the woman is currently pregnant, has recently been pregnant, or is close to menopause. Fertility medications such as human menopausal gonadotropin (hMG), human chorionic gonadotropin (hCG), or clomiphene citrate may also cause inaccurate results. Women taking any of these drugs should consult their physician before using a urinary ovulation prediction test and ask the manufacturer about the medication's effect on the test kit.