An antral follicle count is used to measure a woman's egg supply. We asked a doc to explain what the results can mean.

June 13, 2017

After the season finale of Keeping Up With the Kardashians on Sunday, the famous sisters had us wondering about fertility testing. In case you missed it, Khloé and Kim visited a reproductive specialist because Khloé was considering acting as a surrogate for Kim's third baby, and wanted to make sure that option was a real possibility.

But during an ultrasound of her pelvis, the doctor told Khloé she had fewer ovarian follicles—the fluid-filled structures in which eggs develop—than he would expect in a 32-year-old woman, which could affect her chances of having her own baby. In fact, she might think about freezing her eggs sooner rather than later, he said. The doc told her to stop taking her birth control pills, and come back for another exam.

That did the trick: When Khloé returned for a follow-up, plenty of follicles showed up on the scan. So, how does the pill affect your follicles, exactly? And should any woman who wants a baby one day consider getting the same test Khloé did? To learn more, we spoke with reproductive endocrinologist Daniel B. Shapiro, MD, the chief clinical officer at Prelude Fertility in Atlanta.

RELATED: 15 Factors That Affect a Woman's Fertility

The test Khloé's doctor used it called a basal antral follicle count, he explains: "It tells you how many potential egg sacks would respond to fertility medication in a given cycle." For a woman who isn't undergoing fertility treatment, it can give an indication of her ovarian reserve, or how many eggs she has left.

During a typical menstrual cycle (provided you’re not on the pill), a group of eggs begins to mature, and your ovary and pituitary gland (in your brain) then negotiate to pick the best egg, says Dr. Shapiro. “In your teens and 20s, this is a Miss America-style event where 50 or more eggs stand up and say ‘pick me!’” You’ll ovulate one winning egg, and the rest are destroyed.

But as you age, the contestant pool shrinks. By your mid-30s, you may have less than 20 eggs per cycle, and in your late 30s, less than 10, Dr. Shapiro explains. The follicle count test can tell you how many contestants you currently have.

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Understandably, Khloé left her first appointment worried. But the fact that she was on hormonal birth control would have skewed the result of the test, says Dr. Shapiro. “Being on the pill will make your follicle count look a lot lower than it really is,” he says. Hormonal contraception suppresses FSH, or follicle-stimulating hormone. “The longer you’re on the pill, the less FSH stimulation your follicles will see, so they’re essentially not awake,” he says. They’re there, but you can’t see them, even on a scan.

Go off the pill and you should start to ovulate normally and get your period right away. (If you're over-exercising or don't have enough body fat, it may take up to a year for your period to return, says Dr. Shapiro.)

For women who are curious about their egg reserve, a follicle count might not be the best test, however. The results can vary depending on the doctor who performs it, says Dr. Shapiro. Instead, he recommends an AMH test, a blood test that measures levels of anti-Müellerian hormone, another marker for ovarian reserve. "If you’re not sure what your fertility future holds and not sure when you will be ready to start a family, getting an AMH test is not a bad idea,” he says.