Last year, when their daughter was three, Louisa and Patrick Prendergast* were ready to try in vitro fertilization (IVF) for the second time. They didn’t have any embryos left over from the first round, so they were starting from scratch. The first thing their doctor did was assess Louisa’s ovarian reserve (the number of eggs she had left in her ovaries). “I was nervous about the test results,” says Louisa, who was 40 at the time and fully aware that her pool of eggs was draining.
Women are born with their lifetime supply of eggs, which sit in the ovaries at different stages of development and diminish in quantity and quality with age. Ovarian reserve tests can’t actually count all of the eggs (girls start puberty with about 300,000 eggs, each the size of a grain of sand), but they can estimate how many remain and how well a woman will respond to ovarian-stimulation drugs, which cause more eggs to mature. This can be useful information for those who are considering fertility treatments or freezing their eggs or embryos.
“Ovarian reserve tests are the most important tests of female fertility,” says Beth Taylor, a fertility doctor at Olive Fertility Centre in Vancouver. “If you’re infertile, the tests give you information about how much time you have to conceive and might explain your inability to conceive.”
Ovarian reserve tests (which can involve both a transvaginal ultrasound and blood tests) determine how many eggs have reached an advanced stage of development, which is indicative of the total number of eggs remaining. Every menstrual cycle, in preparation for ovulation, several eggs grow and collect fluid around them in pouches called antral follicles. Usually, only one egg matures enough to be released and the rest die (though in some cases, two eggs are released and you can end up with twins).
To test ovarian reserve, doctors use a transvaginal ultrasound to count those antral follicles and perform blood tests that measure anti-Müllerian hormone (AMH), which is produced by small antral follicles, and follicle-stimulating hormone (FSH), which is known as day-three FSH because it’s typically tested on the third day of the menstrual cycle.
The AMH test is the gold standard, and numerous studies have shown that it’s an accurate predictor of ovarian reserve. The FSH test has fallen out of favour because results fluctuate between cycles, and ultrasound counts can be inaccurate due to the difficulty in spotting apple-seed-size antral follicles. Many clinicians run more than one test and cross-reference the results. While the FSH test is covered by provincial healthcare plans, the AMH test costs between $50 and $200 in jurisdictions where IVF is not funded.
The results of these tests are important to help doctors evaluate the potential benefits of using ovarian-stimulation drugs, which help more antral follicles mature to eggs, which, in turn, increase the odds of conception through sex or intrauterine insemination (IUI) or help fertility specialists retrieve more eggs for IVF. While the average 25- to 34-year-old’s ovarian reserve consists of 15 to 30 antral follicles, fewer than 10 is considered low. The more antral follicles, the more eggs and the more likely a woman is to get pregnant.
“Ovarian reserve is helpful because it tells you if the fertility clinic has a lot to offer you,” says Tom Hannam, an OB/GYN and founder of the Hannam Fertility Centre in Toronto. “If you have a high ovarian reserve, it’s likely that things are going to work out very well. If you have a low ovarian reserve, we can try, but you’re working against the odds.”
The results also help doctors determine the best course of action. “If you have a good egg count, we start with simpler, less expensive, less invasive treatments and work our way up to more aggressive ones like IVF,” says Taylor. “If you have a low egg count, you generally don’t have time to play with. We would certainly encourage those people to consider IVF sooner rather than later.”
But while ovarian reserve tests are effective at estimating ovarian response to stimulation and how much time remains before menopause, they can’t predict a fertile couple’s chances of conceiving. That’s because the number of follicles is irrelevant—you only need one healthy egg to get pregnant. If a woman has a low ovarian reserve, Hannam and Taylor might suggest trying to improve the quality of the remaining eggs as much as possible through lifestyle changes, such as eating well, getting more sleep and taking supplements. “About three months after you make a change, you’ll see it in the eggs,” says Taylor.
Of course, the only test for egg quality is actually trying to get pregnant.
Louisa had all three ovarian reserve tests. Her ultrasound showed that she had eight antral follicles—normal for her age but less than ideal—and her FSH was a bit off target. However, her AMH was barely registering. “It was a big blow,” she says.
Still, Louisa’s doctor encouraged her to go ahead with IVF, saying that the only way to know if treatment would be successful was to try. The couple had already spent about $4,000 on medications, and Louisa had started the injections when they saw another doctor at the clinic who was much less optimistic and gave her a five percent chance of having any response to the drugs based on her AMH level. He asked the couple if they were sure they wanted to continue treatment. “We went home and did a lot of thinking,” says Louisa.
The Prendergasts decided to stick to their plan and are glad they did: They ended up with seven eggs and six embryos and plan to do a frozen transfer when they’re ready.
“For some women, a low ovarian reserve is devastating,” says Louisa. “But sometimes it’s quality over quantity. Ovarian reserve tests should be taken with a big box of salt.”
*Names have been changed