Successful conception depends on the health and supply of a woman’s eggs, making fertility assessment a primary concern for those planning a family or considering assisted reproductive technologies. Individuals seek testing to understand their reproductive timeline and to predict how their ovaries might respond to fertility treatments such as In Vitro Fertilization (IVF). While it is currently not possible to directly measure the genetic health of an unfertilized egg, clinical testing provides powerful insights into the remaining egg pool and overall ovarian function.
Distinguishing Egg Quality from Ovarian Reserve
Current clinical testing measures two distinct aspects of fertility: egg quality and ovarian reserve. Ovarian reserve refers to the quantity or number of eggs remaining in the ovaries, a number that steadily declines throughout a woman’s reproductive lifespan. Egg quality, conversely, describes the viability and genetic integrity of an individual egg, meaning whether it possesses the correct number of chromosomes to develop into a healthy embryo. While the number of eggs (reserve) can be measured with reasonable accuracy using blood tests and ultrasound, the genetic health of an egg (quality) cannot be directly determined until after fertilization. This distinction is fundamental because a woman may have a high number of eggs, indicating a good ovarian reserve, but the majority of those eggs may still possess reduced quality due to age. Conversely, a woman with a diminished ovarian reserve still has the potential to produce a high-quality, chromosomally normal egg. Modern fertility testing focuses on quantifying the reserve to predict the potential response to ovarian stimulation medications.
Hormonal Markers of Ovarian Reserve
The most common initial step in assessing ovarian reserve involves blood tests that measure specific hormone levels. These markers offer an indirect, yet reliable, indication of the size of the remaining egg pool. Anti-Müllerian Hormone (AMH) is one of the most informative hormonal tests because its levels remain relatively stable throughout the menstrual cycle. AMH is secreted by the granulosa cells surrounding the small, developing follicles within the ovaries. The level of AMH in the bloodstream correlates directly with the number of early-stage follicles present, making it a powerful quantitative marker for ovarian reserve. Low levels suggest a diminished ovarian reserve, which may predict a lower yield of eggs during an IVF cycle.
Other hormones, Follicle-Stimulating Hormone (FSH) and estradiol, are typically measured together in a blood draw performed early in the menstrual cycle, usually on day three. FSH is produced by the pituitary gland and signals the ovaries to begin maturing a follicle for ovulation. A high baseline FSH level suggests that the brain must produce an excessive amount of this hormone to prompt the ovaries to function, which is a sign of reduced ovarian responsiveness and a lower egg supply.
Estradiol is measured alongside FSH because an elevated level of estradiol early in the cycle can artificially suppress the FSH reading. If day three estradiol levels are higher than expected, it may mask a true elevation in FSH that would otherwise indicate a diminished ovarian reserve. For these tests to be interpreted accurately, both FSH and estradiol must be within their optimal baseline ranges.
Ultrasound Assessment of Ovarian Reserve
In addition to hormonal testing, a transvaginal ultrasound is performed to gain a visual assessment of the ovarian reserve. This imaging technique is used to conduct an Antral Follicle Count (AFC), which directly estimates the number of resting follicles. Antral follicles are small, fluid-filled sacs within the ovaries, each containing an immature egg. The AFC scan is usually performed early in the menstrual cycle to ensure the ovaries are at their baseline state.
The total number of these follicles across both ovaries is counted by the clinician. This count is a strong predictor of how many eggs a woman is likely to produce in response to fertility medications. A total AFC of 10 to 20 across both ovaries is generally considered a good indication of normal ovarian reserve. Counts below five may suggest a significantly diminished reserve, while high counts can be associated with Polycystic Ovary Syndrome (PCOS). The AFC is frequently used in conjunction with the AMH blood test to provide a comprehensive picture of the current egg supply.
Interpreting Results and Limitations of Direct Quality Assessment
The results from AMH testing, FSH/estradiol levels, and the AFC are collectively used to predict a woman’s reproductive potential, especially her likely response to ovarian stimulation. Low AMH, a low AFC, and an elevated baseline FSH are all indicators of diminished ovarian reserve, which suggests a lower number of eggs will be retrieved during an IVF cycle. This information helps specialists determine the appropriate medication protocol and manage patient expectations for treatment.
However, these tests do not provide the ultimate answer to the question of egg quality, which is the primary determinant of a successful pregnancy. The main limitation of all ovarian reserve tests is that they cannot assess the chromosomal health of the eggs. Egg quality is fundamentally tied to the age of the woman, as the incidence of chromosomally abnormal eggs (aneuploidy) increases significantly over time. Therefore, a woman can have reassuring ovarian reserve test results but still have a low chance of pregnancy if her eggs are genetically compromised.
The only definitive method for assessing egg quality is to observe the egg after retrieval, fertilization, and subsequent development. This quality assessment is performed in the laboratory during an IVF cycle, often through Preimplantation Genetic Testing for Aneuploidy (PGT-A). PGT-A involves biopsying a few cells from a developing embryo and checking the number of chromosomes before the embryo is transferred to the uterus. Without this laboratory process, ovarian reserve tests remain powerful tools for predicting quantity and response to treatment, but they are not a direct measure of the viability of the egg.