Most signs of infertility in women aren’t dramatic or obvious. They show up as subtle changes in your menstrual cycle, unexplained pain, or physical symptoms you might dismiss as unrelated to fertility. The clinical threshold is straightforward: if you’re under 35 and haven’t conceived after 12 months of regular, unprotected sex, or if you’re 35 or older and haven’t conceived after 6 months, that itself meets the definition of infertility. But several warning signs can appear well before you start trying.
Irregular or Short Menstrual Cycles
Your menstrual cycle is one of the most visible windows into your reproductive health. The average cycle length is 29 days, and research from Boston University found that women with cycles of 26 days or fewer had reduced chances of becoming pregnant. Short cycles may reflect a narrower fertile window or signal that ovulation isn’t happening consistently.
Cycles that vary wildly in length from month to month, or periods that disappear for stretches at a time, suggest your body isn’t ovulating on a regular schedule. Ovulation is the non-negotiable event in natural conception, so anything that disrupts it directly affects your ability to get pregnant. Interestingly, the same research found little association between heavy or prolonged menstrual bleeding and reduced fertility, so flow volume alone isn’t a reliable indicator.
When you started menstruating also matters. Women who got their first period before age 12 or after age 15 showed reduced fertility compared to those who started between 12 and 13.
Signs of Hormonal Imbalance
Polycystic ovary syndrome (PCOS) is one of the most common hormonal causes of infertility, and it often announces itself through visible physical changes. Excess androgens (hormones typically higher in men) can cause new hair growth on your face, chin, chest, upper thighs, or back. You might also notice severe acne or thinning hair on your scalp in a pattern similar to male-pattern baldness. These signs can appear years before you try to conceive.
PCOS frequently comes with irregular or absent periods, which circles back to the ovulation problem. If you’re experiencing a combination of unusual hair growth, persistent acne, and unpredictable cycles, that cluster of symptoms points strongly toward a hormonal issue worth investigating.
Pelvic Pain That Goes Beyond Normal Cramps
Most women experience some cramping during their period. But pain that is significantly worse than typical cramps, starts days before your period, or lingers well after bleeding stops can be a sign of endometriosis. This condition, where tissue similar to the uterine lining grows outside the uterus, affects fertility directly. Up to half of women with endometriosis have difficulty conceiving, and for some, infertility testing is how the condition is first discovered.
Other pain patterns to pay attention to include pain during or after sex, and pain during bowel movements or urination that worsens around your period. These aren’t just discomfort to push through. They can point to structural damage, inflammation, or scarring in the reproductive organs that interferes with conception.
Body Weight at Either Extreme
Both underweight and overweight status can shut down ovulation through different hormonal pathways. If your BMI is 18.5 or less, your body may stop producing enough estrogen, which can cause irregular cycles or stop your period entirely. Without ovulation, pregnancy can’t happen.
On the other end, carrying excess weight causes fat cells to release additional estrogen. Too much estrogen can trick your body into behaving as though you’re already on hormonal birth control or already pregnant, suppressing ovulation and stopping your monthly cycle. If your periods have become irregular as your weight has changed in either direction, the two are likely connected.
Changes in Cervical Mucus
This is a subtler sign that most women don’t think to track. In a healthy cycle, cervical mucus changes as you approach ovulation. It shifts from thick and sticky to clear, slippery, and stretchy (often compared to raw egg whites). That stretchy mucus is what allows sperm to travel through the cervix and reach the egg.
If you never notice this change in consistency throughout your cycle, it could mean you’re not ovulating or that your cervical mucus isn’t responding to hormonal shifts the way it should. In some cases, abnormal mucus stays thick through the entire cycle, creating a physical barrier to sperm regardless of whether ovulation occurs. Cervical infections can also damage the mucus environment and, rarely, the body can produce antibodies in the mucus that destroy sperm before they reach the egg.
History of Pelvic Infections
Pelvic inflammatory disease (PID) is the most common preventable cause of infertility in the United States, and it often does its damage silently. PID is a bacterial infection of the uterus, fallopian tubes, and ovaries that can cause internal scarring. That scarring, particularly in the fallopian tubes, can physically block the egg from meeting sperm.
The problem is that PID symptoms can be mild or completely absent. When symptoms do appear, they include lower abdominal pain, foul-smelling vaginal discharge, bleeding between periods, pain during sex, and painful urination. Many women don’t realize they had PID until they have trouble conceiving years later. Treatment can clear the infection, but it cannot reverse scarring that has already formed. If you’ve had a sexually transmitted infection in the past, even one that was treated, there’s a chance it triggered inflammation that left lasting damage.
What Fertility Testing Actually Measures
If any of these signs resonate, fertility testing can provide concrete answers. Two of the most common blood tests measure your ovarian reserve, which is essentially how many eggs you have remaining.
The AMH (anti-Müllerian hormone) test gives a snapshot of your egg supply. Average levels fall between 1.0 and 3.0 ng/mL, with values under 1.0 considered low. To put that in perspective by age: a typical 30-year-old might have an AMH around 2.5 ng/mL, while a 40-year-old might be closer to 1.0 ng/mL. This test can be done on any day of your cycle.
FSH (follicle-stimulating hormone) is measured on day 3 of your cycle. Levels under 10 mIU/mL are considered normal. Between 10 and 15 suggests your egg supply is starting to decline. Consistently above 15 indicates significantly diminished ovarian reserve, and readings above 20 to 25 point to very low egg supply. High FSH means your body is working harder to stimulate your ovaries, which is a sign the ovaries are becoming less responsive.
Age Is the Strongest Predictor
Even without any other signs, age alone significantly affects fertility. A woman in her early to mid-20s has a 25 to 30 percent chance of conceiving in any given month. By age 40, that drops to roughly 5 percent per cycle. This decline is driven primarily by both the number and quality of remaining eggs, and it accelerates after 35.
Age doesn’t cause symptoms you can see or feel, which is what makes it different from every other factor on this list. You can have perfectly regular cycles, no pain, no hormonal symptoms, and still face reduced fertility simply because of where you are in your reproductive timeline. This is why the medical threshold for seeking evaluation is shorter for women 35 and older: six months instead of twelve.