Problems with ovulation – the process of developing an egg suitable for fertilization – is one of the most common causes of infertility. Women are born with all the eggs they will ever have, which are lost constantly until menopause, when the ovarian egg reserve is depleted.
Women over the age of 35 or with a history of prior ovarian surgery may be at risk for diminished ovarian function or reserve (fewer healthy eggs due to natural aging).
The term “ovarian reserve” refers to the reserve of the woman’s ovaries (remaining egg supply). This then is a measure of a woman’s fertility potential in the absence of any problems in the reproductive tract (fallopian tubes, uterus, vagina). It mainly depends on the number and quality of eggs in the ovaries and how well the ovarian follicles are responding to the hormonal signals from the brain.
A strong indicator that a woman is ovulating regularly is having normal and regular menstrual cycles. If a woman has a period quarterly or not at all, she is not ovulating or ovulating too infrequently.
Several tests may help determine whether a woman is ovulating normally. All of these tests check hormone levels, which are the outward signs of ovulation. There are four ovarian reserve tests: follicle-stimulating hormone (FSH) levels, estradiol levels, clomiphene citrate challenge, and ovarian antral follicle count.
Follicle-stimulating hormone (FSH), which helps control a woman’s menstrual cycle and the production of eggs, is tested to determine a woman’s ovarian function and evaluate the quality of her eggs. The test is done on day 3 of the menstrual cycle.
The determination of blood concentrations of follicle-stimulating hormone (FSH) on menstrual cycle day 3 may estimate fertility potential. In general, women with elevated levels of FSH on cycle day 3 have reduced chances of live birth with both ovulation induction and in vitro fertilization (IVF) compared to other women of the same age.
Several laboratory methods are used currently to measure blood levels of FSH. Measurement of levels of these hormones may vary considerably depending upon the particular laboratory method used. Therefore, it may be difficult to compare blood levels that are measured at different laboratories or by different techniques. It is important that normal and abnormal test values be based on the pregnancy rates achieved by women studied at a particular center using the same laboratory methods.
Estradiol is an important form of estrogen, and is tested in conjunction with follicle stimulating hormone (FSH) to measure a woman’s ovarian function and to evaluate the quality of the eggs. Like FSH, it is done on the third day of a woman’s menstrual cycle.
A CCCT provides an additional assessment of ovarian reserve. It is performed by measuring the day 3 FSH and estradiol levels. Then the patient takes Clomid on days 5 through 9, and her FSH is measured again on day 10. The test is considered abnormal if either the day 3 or day 10 FSH values are elevated or if the day 3 estradiol is greater than 80 pg/ml. A poor CCCT test, regardless of patient age, indicates that there will be a decreased response to injectable FSH in assisted reproductive technology cycles. Pregnancy success rates are very low in these women and there is an increased chance of miscarriage.
Antral follicles are small follicles (about 2 to 8 mm in diameter) that can be seen, measured, and counted with ultrasound. Antral follicles are also referred to as resting follicles. Vaginal ultrasound is the best way to accurately assess and count these small structures. Presumably, the number of antral follicles visible on ultrasound is indicative of the relative number of microscopic (and sound asleep) primordial follicles remaining in the ovary. Each primordial follicle contains an immature egg that can potentially develop in the future.
When there are only a few antral follicles visible, there are far fewer eggs remaining as compared to when there are more antrals. As women age, they have less eggs (primordial follicles) remaining and they have fewer antral follicles. Antral follicle counts are a good predictor of the number of mature follicles that could be stimulated in the woman’s ovaries when injectable FSH is used for IVF. The number of eggs retrieved correlates with IVF success rates.
The results of these tests are not absolute indicators of infertility but abnormal levels correlate with decreased response to ovulation induction medications and lowered (IVF) success.