Updated by the Progyny Clinical Team — August 2025.
People with ovaries are born with all the eggs they’ll ever have. Each month, a group of eggs becomes available inside small fluid-filled sacs called follicles. The brain releases a hormone called follicle-stimulating hormone (FSH), which helps one follicle grow that month.
Everyone starts with a different number of eggs, and that number decreases at different rates over time. Genetics, age, medical conditions, and environmental factors all play a role.
Having fewer eggs doesn’t necessarily affect natural fertility if someone is ovulating each month. Ovarian reserve (egg quantity) matters more when fertility treatment is needed or when someone wants to preserve fertility. That’s because treatment can be more efficient when there are more eggs available to stimulate and retrieve.
The most common ovarian reserve tests are:
- Day 3 FSH
- Anti-Müllerian hormone
- Basal antral follicle count by ultrasound
In the past, another test called the clomiphene citrate challenge test (CCCT), or the Clomid challenge test, was also used. This test looks at how the ovaries and brain respond to stimulation. At one time, it was thought to help predict how the ovaries would respond during fertility treatment. But studies have shown that the CCCT is not very accurate. It does not reliably predict treatment response or outcomes. Some insurance plans may require that you take the CCCT before they approve coverage.
How hormone feedback works
The ovaries and brain (specifically, the pituitary gland) communicate through hormones using a system called negative feedback.
At the end of a menstrual cycle, after ovulation, the ovaries stop releasing estrogen and progesterone. That signals the brain to release FSH to start a new cycle. As a follicle grows, it releases estrogen. The rising estrogen level tells the brain to slow down FSH release. This process helps the body choose one dominant follicle to grow and release an egg.
How Clomid works
Clomiphene citrate (Clomid) changes the way the brain responds to estrogen. Normally, estrogen provides negative feedback, telling the brain to lower FSH levels. Clomid binds to the same receptors in the brain as estrogen but does not send that “slow down” signal. The brain doesn’t realize estrogen levels are high and keeps releasing FSH.
This boost in FSH helps follicles grow. In fertility treatment, that can encourage one or more follicles to mature and increase the chances of ovulation.
How the Clomid challenge test works
The CCCT uses this process to test ovarian reserve. People with lower ovarian reserve have fewer follicles and lower levels of certain hormones, such as inhibin. Inhibin normally helps limit FSH release. Without enough inhibin, Clomid can cause an exaggerated rise in FSH that does not come back down quickly.
Here’s how the test is done:
- FSH is measured on day 3 of your menstrual cycle.
- Clomid is taken from days 5 through 9.
- FSH is measured again on day 10.
Most people with normal ovarian reserve have FSH levels that rise and then fall by day 10. If levels stay high, that may be a sign of lower ovarian reserve and a reduced response to stimulation during treatment.
Key takeaways
The CCCT can provide some information about ovarian reserve, but it is less reliable than other tests. It does not predict someone’s ability to get pregnant naturally. Instead, it offers insight into how the ovaries might respond during stimulation.
It’s also important to remember that egg quantity is not the same as egg quality. Both decline with age, but not always at the same rate.
If you have questions or concerns, Progyny is here for you. Please contact your Progyny Care Advocate for support.
Disclaimer: The information provided by Progyny is for educational purposes only and is not medical advice. Always consult a qualified healthcare provider for medical guidance.