Low ovarian reserve means your ovaries contain fewer eggs than expected for your age. It’s diagnosed when Anti-Mullerian Hormone (AMH) levels fall below 1.0 ng/mL, with levels at or below 0.4 ng/mL considered severely low. While every woman’s egg supply naturally declines over time, several factors can speed up that process or cause you to start with fewer eggs in the first place.
Age Is the Primary Driver
Women are born with all the eggs they’ll ever have, typically around one to two million. By puberty, that number has already dropped to roughly 300,000 to 400,000. From there, the supply declines steadily with each menstrual cycle and through a constant background process of follicle loss that happens regardless of whether you ovulate. The steepest drop tends to begin in the mid-to-late 30s, and by the early 40s, both egg quantity and quality have declined significantly. This is the most common reason for low ovarian reserve, and it’s entirely normal biology.
That said, some women experience this decline much earlier than expected. When ovarian reserve is low relative to age, the causes below are worth investigating.
Genetic Factors
Your genes play a larger role in ovarian reserve than many people realize. In a study of 120 women with diminished ovarian reserve, genetic testing identified a likely cause in about 24% of cases. The genes involved fell into several categories: those affecting cell energy production and mitochondrial function (about 30%), follicle growth (24%), DNA repair (19%), and cellular aging (16%).
One finding stood out. Women whose low reserve was linked to DNA repair gene mutations had notably poor outcomes: none achieved pregnancy, suggesting these genes affect not just egg quantity but egg quality in ways that are difficult to overcome.
Certain inherited conditions also carry risk. Turner syndrome, where a woman is missing part or all of one X chromosome, is a well-known cause of early egg depletion. The FMR1 gene premutation, which is linked to Fragile X syndrome in offspring, has been investigated as a potential contributor, though the evidence remains mixed. In some cases, low ovarian reserve is part of a broader genetic syndrome affecting multiple organ systems, not just the ovaries.
Chemotherapy and Radiation
Cancer treatment is one of the most significant medical causes of low ovarian reserve. Certain chemotherapy drugs directly destroy the pool of immature follicles in the ovaries. Cyclophosphamide, an alkylating agent used in many cancer regimens, is among the most damaging. It causes significant, lasting reductions in primordial and primary follicles, the earliest-stage eggs that represent your future supply.
Other drug classes once considered safer may also pose real risks. Research on irinotecan, a drug used in colorectal and other cancers, found that it caused irreversible loss of ovarian reserve comparable to cyclophosphamide. Both drugs reduced AMH levels long-term and depleted the markers that indicate healthy early-stage follicles, with damage still measurable three months after treatment.
Radiation therapy to the pelvic area carries similar risks. The degree of damage depends on the dose and how close the radiation field is to the ovaries. This is why fertility preservation options like egg freezing are discussed before treatment when possible.
Ovarian Surgery
Surgery on the ovaries, even for benign conditions, can reduce your egg reserve. Laparoscopic cystectomy, where a cyst is surgically removed from the ovary, causes a measurable drop in AMH. In one prospective study, average AMH fell from 5.1 ng/mL before surgery to 3.4 ng/mL three months afterward. This decline happened whether the cyst was an endometrioma (a cyst caused by endometriosis) or another type of benign cyst.
The biggest predictor of how much reserve you lose isn’t the type of cyst. It’s whether the surgery involves one ovary or both. Bilateral surgery, operating on both ovaries, was the only significant factor predicting steeper AMH decline. This is why surgeons often weigh the benefits of cyst removal against the potential cost to fertility, particularly in younger women who haven’t yet had children.
Autoimmune Conditions
Your immune system can sometimes target the ovaries by mistake, a condition called autoimmune oophoritis. The immune attack damages ovarian tissue and accelerates the loss of follicles. This can occur on its own but more often appears alongside other autoimmune diseases. Conditions associated with autoimmune oophoritis include Addison’s disease (adrenal insufficiency), lupus, pernicious anemia, myasthenia gravis, and autoimmune polyglandular syndromes types I and II.
If you have one autoimmune condition and are experiencing signs of low ovarian reserve, such as irregular periods or difficulty conceiving, the connection is worth exploring with your doctor. Autoimmune oophoritis can sometimes be identified through specific antibody testing.
Endometriosis
Endometriosis affects ovarian reserve through two pathways. The disease itself creates a chronic inflammatory environment in the pelvis that can damage ovarian tissue over time. Endometriomas, the chocolate-colored cysts that form on the ovaries, physically displace healthy ovarian tissue and may compress surrounding follicles. Then, as described above, the surgery often needed to treat endometriomas removes additional healthy tissue along with the cyst wall, compounding the loss.
Environmental Toxins
A growing body of evidence links certain chemicals to ovarian damage. These endocrine disruptors interfere with the hormones that regulate follicle development and egg maturation.
- BPA (bisphenol A), found in some plastics and can linings, alters how genes in the ovary are activated and deactivated, impairing follicle development and reducing egg quality.
- Phthalates, used in plastics, cosmetics, and fragrances, disrupt hormone levels and follicle growth. Animal research on the phthalate DEHP showed that prenatal exposure not only affected the exposed generation but accelerated reproductive aging in granddaughters and great-granddaughters.
- Pesticides like DDT and methoxychlor interfere with estrogen and progesterone production in the cells surrounding developing eggs, leading to follicle death or chromosome errors in the eggs themselves.
The multigenerational effects are particularly striking. Chemical exposures your mother or grandmother experienced during pregnancy may influence the ovarian reserve you were born with.
Smoking
Cigarette smoke contains hundreds of toxic compounds that accelerate egg loss. The chemicals damage DNA in developing follicles and disrupt the blood supply to the ovaries. The effect is measurable at the population level: women who smoke reach menopause more than a year earlier on average than women who never smoked (47.8 years versus 48.9 years in one large population study). That year represents thousands of additional follicles lost prematurely. The damage appears to be cumulative, meaning the longer and more heavily you smoke, the greater the impact on your remaining egg supply.
How Low Ovarian Reserve Is Detected
The primary screening tool is an AMH blood test, which can be drawn on any day of your menstrual cycle. AMH is produced by small, growing follicles in the ovaries, so lower levels reflect a smaller remaining pool. Average levels fall between 1.0 and 3.0 ng/mL. Levels below 1.0 ng/mL are considered low, and levels at or below 0.4 ng/mL are severely low.
Doctors also use antral follicle count, an ultrasound measurement of the small follicles visible on both ovaries early in a menstrual cycle, and day-3 FSH levels. FSH rises as ovarian reserve drops because the brain has to work harder to stimulate follicle growth. These three markers together give the clearest picture, though none of them can tell you the exact number of eggs remaining or predict whether you’ll conceive naturally. They’re estimates of the overall trend.