The Guide to Ovarian Reserve Testing
Many factors can affect a couple’s ability to conceive naturally, including hormonal imbalances, irregular ovulation, and a decline in oocyte quality. As women age, their ovarian reserve, the number of oocytes left in their ovaries, naturally decreases. This can make it challenging to get pregnant and can also lead to a poorer response to fertility medications, potentially resulting in nonoccurrence of pregnancy.
Fertility clinics often perform ovarian reserve testing (ORTs) to help identify individuals who may be at higher risk of these challenges. These tests can provide valuable information about a woman’s remaining oocytes and potential responsiveness to fertility drugs. Clinicians can then guide treatment decisions, such as pursuing egg freezing or in vitro fertilization (IVF).
This article will explore ovarian reserve testing in more detail, explaining what it is, why it is done, and the different types of tests available. We will also discuss what to do if your test results suggest diminished ovarian reserve.
Ovarian reserve is the number of oocytes remaining in the ovaries (or in the ovary in cases when one ovary has been removed), also known as “oocyte quantity” (oocyte number). Ovarian reserve, or oocyte quantity, is different from oocyte quality, which affects the potential of a fertilized oocyte to result in a viable embryo, then a fetus, and finally, in a live–born newborn.
By the 4th–5th month of pregnancy (around 16–20 weeks of gestation), germ cell numbers reach a peak — the female fetus has ∼6–7 million oocytes in her ovaries. However, a natural process where oocytes don’t develop fully (follicle atresia) begins between weeks 19–22, leading to the diminishing of the ovarian reserve. By the time the baby is born, the number of oocytes is steadily reduced — depending on the initial number of oocytes, the decrease by birth can be between 83.33% (if born with 1 million oocytes) and 92.86% (if born with 500,000 oocytes).
Female infants are born with ∼500,000 to 1 million oocytes, but some newborns may have up to 2 million oocytes left in their ovarian reserves. If a baby girl is born with 2 million oocytes, this represents a decrease of approximately 66.67% from the peak number of oocytes during the prenatal stage (6 million).
After birth, the number of oocytes continues to decline. By the late teens (18–19 years old), a young woman has around 300,000 to 400,000 oocytes left in her ovarian reserve. By the early 20s, this number diminishes to around 160,000 to 300,000. By the late 20s, the oocyte count is around 100,000 to 150,000. By the early 30s, it decreases to around 70,000 to 100,000, and by the late 30s, the number of oocytes declines to approximately 25,000 or fewer. This significant reduction in oocyte count leads to increasing negative scenarios, such as a higher likelihood of miscarriage, increased difficulty in conceiving, and a greater risk of chromosomal abnormalities in the fetus. Additionally, the chances of requiring fertility treatments, such as in vitro fertilization (IVF), rise substantially, and the overall success rates of these treatments decrease as the ovarian reserve diminishes.
Normal ovarian reserve refers to a situation where a woman of reproductive age has a typical number of eggs in her ovaries for her age. This number can vary slightly between individuals but generally translates to a higher chance of natural conception. It also signifies a more favorable response to fertility treatments like ovulation induction or in vitro fertilization (IVF) if needed in the future.
Here is a breakdown of what a “normal” ovarian reserve might look like:
Factors affecting normal ovarian reserve:
It is worth noting that normal ovarian reserve doesn’t guarantee fertility. Other factors like a partner’s sperm health and overall reproductive health can also play a role. However, having a normal ovarian reserve increases a woman’s chances of conceiving naturally or with the help of fertility treatments.
Diminished ovarian reserve (DOR) refers to a condition where a woman of reproductive age (typically under 39) has a lower–than–expected number of eggs in her ovaries. She may have regular menses, but her response to ovarian stimulation or fertility is lower compared with women of her age. Decreased ovarian reserve affects female fertility and makes it more difficult to get pregnant. It is essential to distinguish DOR from menopause, which is the natural end of a woman’s menstrual cycle, and premature ovarian insufficiency (POI), where menopause occurs before age 40.
In most cases, the cause(s) of diminished ovarian reserve are unknown. Scientists aren’t entirely sure what causes DOR. It could be due to several factors: a pathologic condition resulting from abnormally rapid atresia (oocytes dying off faster than usual) in normal ovarian reserves oocytes, from normal atresia of an abnormally small ovarian reserve (some women simply have a lower initial number of oocytes. Thus, they are starting with fewer oocytes than average), or just natural variations in oocyte quantity (the number of oocytes women have can vary naturally), and DOR might be on the lower end of that range.
A loss of oocytes and fertility potential can be the result of pelvic irradiation, systemic chemotherapy, autoimmune factors, ovarian surgery, and genetic abnormalities (Fragile X Premutation (FMR1 pre–mutations) — a mutation in the FMR1 gene that doesn’t cause Fragile X syndrome itself but can increase the risk of DOR, 45,X chromosomal mosaicism known as Turner Syndrome — a chromosomal abnormality where a female has only one X chromosome instead of the usual two).
Diagnosis of decreased ovarian reserve (DOR) often involves:
The key difference between normal and low ovarian reserve lies in the number and quality of oocytes remaining in the ovaries. Women with normal ovarian reserve have a higher chance of getting pregnant naturally. Conversely, women with DOR may face challenges in conception and might require fertility treatments like in vitro fertilization (IVF) for a higher success rate.
It is essential to note that DOR doesn’t indicate infertility, and many women with the condition can still conceive naturally. Early diagnosis and consultation with a fertility specialist can help explore all available options for achieving pregnancy.
Ovarian reserve tests, which are the tools in assessing a woman’s fertility potential, provide an estimate of her remaining oocytes. These tests, including both biochemical (blood) tests and ultrasound scans of the ovaries, are designed to measure the oocyte or follicular pool. Biochemical tests of ovarian reserve, such as early–follicular–phase measurements of follicle-stimulating hormone (FSH), Estradiol (E2), or inhibin B; measurement of Antimüllerian hormone (AMH); and provocative tests like the clomiphene citrate challenge test (CCCT), are specifically intended for this purpose.
Inhibin B and Antimüllerian hormone (AMH) are protein–sugar molecules (glycoproteins) known as glycoprotein hormones produced by immature follicles in the ovaries. Because these hormones come from the follicles themselves, they directly reflect the number of follicles a woman has remaining. While AMH comes mainly from early-developing follicles (primary, preantral, and early antral follicles), inhibin B is produced mostly by follicles in a slightly later stage (preantral follicles). As a woman ages and her follicles decrease, both AMH and inhibin B levels drop. This decline in inhibin B disrupts a signaling system that normally keeps FSH in check. As a result, FSH levels rise, which, in turn, triggers follicles to develop sooner and estrogen to increase. This leads to shorter follicular phases and menstrual cycles overall. Because of this, these hormone tests can indicate a woman’s remaining oocytes.
Follicle-stimulating hormone (FSH) is a key gonadotrophic hormone, produced by the pituitary gland that plays a key role in female fertility. It stimulates the growth and development of ovarian follicles, the small fluid–filled sacs that “host” immature oocytes within the ovaries. FSH specifically helps some follicles mature from antral follicles into dominant follicles, which eventually release a mature oocyte (in some cycles one ovary may release more than one oocyte or both ovaries may release oocytes) during ovulation. FSH also signals the ovaries to produce estrogen. This estrogen, in turn, provides feedback to the pituitary gland, regulating FSH production and promoting the growth of the endometrium, the lining of the uterus, which prepares for a potential pregnancy.
If the ovaries are not working normally, as is the case of premature ovarian insufficiency (POI), the level of FSH in the blood increases. To account for natural cycle variability, the clinician may do two FSH tests at least a month or a month-and-a-half apart. If the FSH level in both tests is high, then a diagnosis of POI becomes more likely. However, other factors can also elevate FSH levels so that additional tests may be necessary for confirmation. These might include estradiol testing, which measures estrogen levels, or pelvic ultrasound to assess the number of remaining follicles.
Estradiol (E2) is the most potent and prevalent form of the three major naturally occurring estrogens (estrone, E2, and estriol). Produced primarily in the ovaries, basal E2 levels, measured in a blood test, play a vital role in regulating ovulation. E2 levels surge just before ovulation, triggering the release of a mature oocyte(s). Beyond ovulation, E2 also influences the development of female secondary sex characteristics, such as breast development and fat distribution. Additionally, E2 works with other hormones to regulate the menstrual cycle and maintain bone health. However, E2 levels naturally fluctuate throughout the menstrual cycle, reaching their peak just before ovulation and dropping significantly afterwards. This is why the timing of the E2 test can impact the results. Healthcare providers typically recommend testing during the early follicular phase (cycle days 2–5) for better consistency when evaluating ovarian function.
To assess ovarian reserve, fertility specialists measure FSH and E2 levels in the early follicular phase (days 2–5 of the menstrual cycle). While an elevated FSH can indicate diminished ovarian reserve (DOR), it is not a perfect test. And here is why:
Despite its limitations, FSH is commonly used as an ovarian reserve test, and high values have been associated with both poor ovarian response and failure to achieve pregnancy. Measurement of both FSH and estradiol on cycle day 3 may help decrease the incidence of false–negative testing in ovarian reserve testing.
Inhibins (inhibin A and B) are protein hormones secreted by granulosa cells of the ovaries. They play a role in regulating the menstrual cycle by limiting the amount of follicle–stimulating hormone (FSH) produced by the pituitary gland. FSH, in turn, helps oocytes mature in the ovaries. In addition to their role in the pituitary gland, inhibins may also have other effects within the ovaries themselves.
Healthy ovaries produce different amounts of inhibin A and B throughout the menstrual cycle. Inhibin A is mostly produced by the dominant follicle and corpus luteum after ovulation (when an oocyte is released) and reaches its peak level in the middle of the cycle. Inhibin B, on the other hand, is primarily produced by small developing follicles. It increases early in the cycle when oocytes are starting to develop, coinciding with a decrease in FSH, a hormone that helps oocytes mature. This suggests that inhibin B might play a role in controlling this process.
In contrast to inhibin A, inhibin B levels increase early in the follicular phase, reaching a peak coincident with the onset of the mid–follicular phase decline in FSH levels. These levels then decrease in the late follicular phase with a short–lived peak 2 days after the mid–cycle luteinizing hormone (LH) peak. Inhibin B remains low during the luteal phase. The rise of inhibin B early in the cycle coincides with a decrease in FSH, suggesting it directly suppresses FSH production to regulate folliculogenesis (oocyte development). Finally, at menopause, with the depletion of ovarian follicles, serum inhibin A and B levels decrease to very low or undetectable levels.
Inhibin B is a peptide hormone that is produced primarily by growing pre-antral and early antral follicles that are responsive to FSH. As the follicle continues to grow and become dominant, inhibin B secretion declines. With aging, the number of these growing follicles decreases, leading to lower inhibin B levels. This decrease is associated with higher FSH levels, decreased oocyte quality, and lower fertility potential. High levels of Inhibin B indicate a good ovarian reserve, while low levels may suggest a diminished ovarian reserve. Therefore, Inhibin B can be a fertility test, along with FSH, to assess a woman’s ability to conceive by reflecting the number of growing follicles in her ovaries.
Luteinizing hormone is one of the hormones produced by the pituitary gland that plays a vital role in ovulation. LH levels remain low throughout most of the menstrual cycle. But once a developing follicle becomes dominant and reaches a specific size — usually around the middle of the cycle — LH secretion surges to really high levels. A surge in LH triggers the release of a mature oocyte from the ovary, known as “ovulation,” about 24 to 36 hours later.
After the oocyte is released, the empty follicle on the ovary transforms into a structure known as the “corpus luteum.” The corpus luteum then begins to secrete progesterone, a hormone crucial for preparing the lining of the uterus for a potential pregnancy. The corpus luteum has a lifespan of about 14 days. If pregnancy occurs, the developing embryo produces a hormone called human chorionic gonadotropin (hCG), which sustains the corpus luteum and its progesterone production. However, if pregnancy doesn’t occur, the corpus luteum shrivels up, stopping progesterone secretion and triggering a menstrual period.
The luteinizing hormone (LH) fertility test measures the level of LH in a woman’s bloodstream. This test can be particularly beneficial for women with irregular menstrual cycles, as it provides a more objective marker of ovulation timing compared to solely relying on cycle length predictions. It can also be used to investigate the cases of suspected high LH levels that indicate that the follicles are not functioning normally. It can also be used in conjunction with other fertility tests, such as basal body temperature charting or ultrasound monitoring, to create a more comprehensive picture of a woman’s reproductive health. While not definitive on its own, the LH fertility test offers a valuable tool for couples trying to conceive.
The luteinizing hormone (LH) fertility test measures the level of LH in a woman’s bloodstream. This test can be particularly beneficial for women with irregular menstrual cycles, as it provides a more objective marker of ovulation timing compared to solely relying on cycle length predictions. It can also be used to investigate the cases of suspected high LH levels that indicate that the follicles are not functioning normally. It can also be used in conjunction with other fertility tests, such as basal body temperature charting or ultrasound monitoring, to create a more comprehensive picture of a woman’s reproductive health. While not definitive on its own, the LH fertility test offers a valuable tool for couples trying to conceive.
Antimüllerian hormone (AMH) is a glycoprotein produced by granulosa cells of preantral (primary and secondary) and small antral follicles (AFs) in the ovaries.
The ovaries begin producing AMH in utero at about 36 weeks of gestation; its levels rise in the teens and peak at about 25 years of age, then decline until reaching undetectable levels a few years before menopause.
Antimüllerian hormone (AMH) production is initiated as ovarian follicles transition from their earliest (primordial) stage to the primary stage. These developing follicles continuously produce AMH until they reach a specific size range, typically 2–6 mm in diameter, known as the antral stage. Interestingly, detectable levels of AMH decline as follicles mature and grow beyond this size. In healthy women, AMH becomes undetectable in larger follicles (greater than 8–10 mm).
This relationship between AMH production and follicular size reflects the underlying biology. The number of small antral follicles (AFs) directly correlates with the initial pool of primordial follicles, a woman’s initial oocyte reserve (a predictive marker of oocyte quantity but not quality). As these small AFs diminish with age, AMH production declines, eventually becoming undetectable around menopause.
During a fertility workup, the AMH test is considered the most sensitive and earliest indicator of ovarian reserve. It is a predictive marker of ovarian response to gonadotropin stimulation, including both poor response (not producing enough oocytes) and an excessive response (leading to a complication called ovarian hyperstimulation syndrome, or OHSS). This is because AMH levels directly reflect a woman’s ovarian reserve, which in turn influences her response to fertility medications and overall fertility potential. In women with ultralow AMH (<0.16 ng/mL), there is a significantly higher cycle cancellation rate during fertility treatments. Additionally, declining AMH levels indicate approaching perimenopause and menopause as they naturally decrease with age.
A key advantage of AMH testing is its cycle independence. Unlike many other fertility biomarkers, AMH levels remain consistent throughout the menstrual cycle, allowing for measurement on any day. This eliminates the need for complex cycle tracking and provides a convenient tool for assessing ovarian reserve.
The Clomiphene Citrate Challenge Test (CCCT) is a fertility test used to assess a woman’s ovarian reserve, which is the number and quality of her eggs. It involves taking a medication called clomiphene citrate for five days (days 5–9 of the menstrual cycle) and measuring hormone levels (FSH) at two times in the menstrual cycle: on day 3 (baseline) and day 10 (stimulated). Abnormal FSH levels detected on day 3 or day 10, or both, indicate a potential decrease in ovarian response.
It involves administering a medication called clomiphene citrate for five days (days 5–9 of the menstrual cycle) and measuring blood levels of follicle-stimulating hormone (FSH) at two points: on day 3 (baseline) and day 10 (stimulated). Abnormal FSH levels on either day or a combination of both suggests a potential decrease in ovarian response. However, while the CCCT can identify potential problems with egg quality, recent research suggests that it may not be more accurate than a simpler blood test. Additionally, the Clomiphene Citrate Challenge Test can be expensive, time–consuming and come with side effects due to the medication. Therefore, it is not routinely recommended.
The Antral Follicle Count Test (AFC) has long been used to assess a woman’s fertility potential by measuring tiny fluid sacs in the ovaries using a transvaginal ultrasound scan early in her menstrual cycle. The number of these sacs, called antral follicles, can indicate how many oocytes a woman has left. Generally, a lower AFC suggests fewer oocytes, while a higher AFC suggests more oocytes.
While specific numbers can vary, the results provide valuable insights: A very low AFC (very few follicles) indicates a low response to fertility medications, potentially leading to a canceled cycle. A moderate AFC (3–6 follicles) suggests a possible low response. An average AFC (7–10 follicles) is typically associated with a good response to stimulation medications. Finally, a high AFC (more than 14 follicles) can be a sign of potential hyperresponse to fertility medications.
Ovarian volume is another potential indicator of a woman’s ovarian reserve, which refers to the number and quality of her remaining oocytes. Variation in ovarian volume is normal and can occur naturally between the two ovaries. However, ovarian volume generally declines with age. This is why measuring ovarian volume can be a helpful tool in fertility evaluation. The measurement itself is performed using ultrasound technology and involves calculating the volume of each ovary in three different planes.
In conclusion, understanding ovarian reserve and its testing is essential for individuals and couples navigating fertility challenges. As age advances, the number and quality of oocytes decline naturally, impacting fertility potential. Ovarian reserve testing, through methods such as measuring AMH, FSH, and antral follicle counts, offers valuable insights into a woman’s reproductive health and informs decisions regarding fertility treatments like IVF or egg freezing. By providing early identification of diminished ovarian reserve, these tests empower individuals and couples to explore proactive fertility strategies and seek appropriate medical guidance, ensuring personalized care tailored to their unique reproductive needs and goals.
It is worth noting that no single test is perfect for evaluating ovarian reserve. Fertility specialists may recommend a combination of tests for a more accurate picture. Additionally, a diagnosis of DOR (Diminished Ovarian Reserve) doesn’t necessarily mean infertility. Other factors, such as sperm health, overall reproductive health, and the age of both partners, also play a significant role. However, ovarian reserve testing remains a crucial tool for establishing a baseline and guiding treatment plans, offering valuable information for informed decision–making about family planning.
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