What can ovarian reserve testing really tell us?
Infertility is what medical experts call a “functional” diagnosis. That means the only way someone can be diagnosed as infertile is if they don’t or can’t get pregnant—or get their partner pregnant—after 12 months of trying.
It makes sense, then, that there’s a lot of appeal to the idea of a fertility test; wouldn’t it be great if women could know their chances of getting pregnant before they start trying? That could help them plan better, jump straight to fertility treatments if they’ll need them, or freeze their eggs earlier to prepare for the difficulty they might have getting pregnant later.
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So-called “fertility tests” do exist; they’re more formally—and in a crucial way, as we’ll see in moment, more precisely—known as ovarian reserve tests. But as recent studies demonstrate, and most reproductive endocrinologists understand, ovarian reserve tests, while important for many reasons, can’t accurately predict your chance of getting pregnant, because they only tell one side of the story.
Let’s dive in.
What is ovarian reserve testing?
Ovarian reserve—a fancy word for egg count—testing typically takes the form of an AMH, or anti-Mullerian hormone, blood test and an antral follicle count.
AMH is a protein hormone produced by cells inside the ovarian follicles; the level of AMH in the blood can help doctors estimate the number of follicles inside the ovaries. An antral follicle count, on the other hand, is performed by a doctor during an ultrasound. After visualizing the ovaries, the doctor can count the “activated” follicles, and use that number to estimate a woman’s total ovarian reserve.
Older, and generally less accurate, methods of measuring ovarian reserve include FSH, estradiol, and inhibin testing on the third day of the menstrual period. FSH, or follicle-stimulating hormone, is a chemical that helps the ovarian follicle become mature and release an egg. In contrast to AMH, high FSH levels are associated with a low ovarian reserve.
Learn more about egg count.
These tests have been called critical and important by many fertility advocates and medical professionals. But in a recently published study of 750 women attempting to get pregnant, researchers determined that women with low AMH levels (less than 0.7ng/ml) and/or high FSH levels (more than 10 mIU/mL in a blood test) don’t have a significantly lower (or higher!) chance of getting pregnant in a 12-month period than women with typical hormone levels.
What’s going on?
Egg count vs. egg quality
As we mentioned above, these ovarian reserve tests tell us about a woman’s egg count, which is one factor in fertility. But the other—and for purposes of natural fertility, more important—factor in whether a woman can get pregnant, stay pregnant, and deliver a healthy baby is egg quality. Egg quality refers to whether an egg is genetically “normal” (euploid) or abnormal (aneuploid); abnormal eggs will lead to infertility, miscarriage, or genetic disorders such as Down syndrome.
Learn more about egg quality.
The percentage of normal vs. abnormal eggs is directly related to age; younger women will have mostly normal eggs, while older women will have mostly abnormal eggs.
So as our chief medical officer Dr. Joshua Klein explains it, “the decline in natural fertility with age is actually driven primarily by egg quality.” Regardless of a woman’s egg count—whether her AMH and FSH levels are low or high—she’ll naturally ovulate one egg per month, “not more, not less,” he says. So the chance of natural pregnancy depends directly and exclusively on “the chance that this month’s egg is a healthy one”—not on how many are left in the reserves for the future.
(Enter your email at the bottom of this page to get Dr. Klein’s entire white paper on the biological clock.)
The truth is that there’s no test for egg quality that can be done in advance. The only tests for euploidy are genetic tests that can be performed on embryos after they’re already fertilized and developed, not on eggs.
However, there is a direct relationship, well-supported in scientific literature, between a woman’s age and the number of normal embryos created from her eggs (see the chart above). That allows doctors to use age as the primary estimator for how many healthy eggs a woman has, and for her chance of ovulating a healthy egg in any given month.
Learn more about fertility and age.
What ovarian reserve testing can’t tell us
The importance of egg quality explains why ovarian reserve testing alone can’t estimate a woman’s chances of getting pregnant in a given month.
Even if a 40-year-old woman has lots of eggs left—a high ovarian reserve for her age—if 75% of those eggs are abnormal (as is typical), she’s going to have a difficult time getting pregnant. And vice versa: if a 25-year-old woman has a low ovarian reserve for her age according to her test results, she still has a pretty good chance of getting pregnant, because it’s likely that 75% or more of her eggs are genetically normal. This is why experts, like our doctors here at Extend Fertility, recommend egg freezing before age 35.
What ovarian reserve testing can tell us
On the other hand, ovarian reserve testing does have some important uses in fertility medicine. These tests can tell us when a woman is getting close to menopause; a sustained high level of FSH in the blood or urine, along with a lack of a period, is often used to confirm menopause, and AMH levels are strongly tied to time until menopause. As Dr. Klein explains, “one thing your tests can tell us is whether you are at risk for early menopause.”
AMH testing and antral follicle count can also indicate other potential reproductive issues, such as polycystic ovarian syndrome (PCOS), which, being characterized as a condition in which a woman’s ovaries develop many follicles but don’t actually release an egg, is typically associated with abnormally high AMH and specific signs on an ultrasound.
Additionally—and importantly, for women considering egg freezing—a woman’s egg count directly affects her chance of success with egg freezing and in vitro fertilization.
That’s because egg freezing and IVF success rates are directly tied to the number of eggs doctors can retrieve in any given cycle. Women with a higher ovarian reserve are more likely to respond robustly to the hormone medication used in these fertility treatments, producing more eggs in a single cycle than women with a lower ovarian reserve.
Learn more about egg freezing success rates.
Let’s say a woman doing an egg freezing cycle produces 15 eggs; 80–90% of those eggs are likely to be mature, and about 90% of the eggs frozen are likely to survive the thaw, leaving about 12 eggs. The percentage of those eggs that fertilize and are able to create a healthy pregnancy will depend on the woman’s age at the time of freezing, but the pool she has to work with is higher than a woman with a lower ovarian reserve, who maybe froze 7 or 8 eggs in a cycle.
And it’s important to mention that, while there’s a high variability in egg count among women of the same age, ovarian reserve in an individual woman is also tied to age. (See the relationship between AMH and age below.) So any individual woman will likely have a higher ovarian reserve—and therefore be more likely to produce more eggs in a single cycle—when she’s under 35, which is another reason we recommend egg freezing for women in their early 30s.
The best way to understand ovarian reserve: in context.
Ovarian reserve is part of the overall picture of your fertility health. Your age, lifestyle, and medical history are also important factors in determining how likely you are to get pregnant. Too often, women get their “numbers” without a true analysis of what those numbers mean for them personally, or their fertility and family goals. The best way to understand this information is with the guidance of a fertility expert, like the doctors and nurses on our healthcare team.
If you’re interested in understanding your fertility health, we’re here to help. Contact us.