The Clomid challenge test (clomiphene citrate challenge test) is a good indicator of "ovarian reserve". A woman is born with a lifetime supply of eggs within her ovaries and as she ages the "quality" of her eggs naturally declines. Sometimes this decline occurs early due to perimenopause, genetics, and/or unknown factors.
One of the first indications of declining egg quality is a high FSH measurement on day 3 of the cycle. If this is high, the infertility specialist will often order the clomid challenge test.
The Clomid challenge test (CCCT) provides an additional measurement of ovarian reserve. The CCCT is performed by measuring the day 3 FSH and estradiol levels, the patient takes 100 mg of Clomid on cycle days 5-9, and her FSH is measured again on day 10. The test is 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.