Infertility affects men and women at surprisingly similar rates. When couples struggle to conceive, roughly 30% of cases trace back to female factors alone, 20% to 30% to male factors alone, and about 30% remain unexplained even after thorough testing. The rest involve problems in both partners. So neither sex is dramatically “more likely” to be infertile, though female-factor diagnoses are identified slightly more often in clinical settings.
That said, the biology behind infertility looks very different in men and women, and age, lifestyle, and environmental exposures hit each sex in distinct ways.
How Infertility Breaks Down by Cause
The traditional framing that infertility is “a woman’s problem” is outdated. Male factors account for 20% to 30% of all infertility cases on their own, and when you include couples where both partners have contributing issues, men play a role in close to half of all cases. The reason female-factor infertility gets diagnosed more often isn’t necessarily because it’s more common. It’s partly because women’s reproductive health is tested more routinely and more thoroughly during fertility workups.
About 30% of infertile couples receive no clear diagnosis at all. Unexplained infertility is only labeled after both partners show apparently normal results: regular ovulation, open fallopian tubes, a healthy uterus, and a normal semen analysis. Couples need at least 12 months of regular unprotected sex before that label applies.
Common Causes in Women
Ovulation problems are the single biggest category, responsible for 25% to 40% of female infertility cases. Polycystic ovary syndrome (PCOS) drives about 70% of those ovulation failures. PCOS disrupts the hormonal signals that trigger egg release each month, and it’s one of the most treatable causes of infertility in women.
Blocked or damaged fallopian tubes account for another 20% to 35% of cases. Pelvic infections, prior surgeries, and endometriosis can all scar or obstruct the tubes. Endometriosis itself, where tissue similar to the uterine lining grows outside the uterus and causes inflammation, contributes to 10% to 15% of female infertility cases independently. It creates adhesions that distort pelvic anatomy and interfere with egg transport.
As women age, conditions like uterine fibroids, tubal disease, and endometriosis become more common, compounding the natural decline in egg quality and quantity.
Common Causes in Men
Most male infertility traces back to sperm production or function. Low sperm count, poor sperm movement, and abnormally shaped sperm are the most frequent findings. In some men, semen contains no sperm at all, a condition called azoospermia.
Varicocele, a swelling of veins in the scrotum that raises testicular temperature, is one of the most common correctable causes. Genetic conditions can also play a role. Infections of the reproductive tract, including sexually transmitted infections, sometimes damage the structures that produce or transport sperm. Chronic conditions like diabetes and certain autoimmune disorders where the immune system attacks sperm cells are less common but well-documented contributors.
Unlike female infertility, male infertility often produces no obvious symptoms. A man with a very low sperm count typically feels perfectly healthy, which is one reason male-factor infertility goes underdiagnosed.
How Age Affects Each Sex Differently
Age is the single biggest dividing line between male and female fertility, and it’s where the two sexes genuinely diverge. Women are born with all the eggs they’ll ever have, estimated at 1 to 2 million at birth. That number drops continuously throughout life, and the decline in both egg count and egg quality accelerates significantly after the mid-30s. After menopause, natural conception is no longer possible.
As eggs age, they’re more likely to carry chromosomal abnormalities. This raises the risk of miscarriage and of conditions like Down syndrome. It also means that even with fertility treatment, success rates drop meaningfully once a woman passes 40.
Men don’t face the same hard cutoff. They continue producing sperm throughout life, but sperm quality does decline with age. Older men produce fewer sperm, and the sperm they do produce carry more genetic abnormalities. Testosterone levels gradually fall, which can contribute to erectile difficulties. Testicle volume decreases, and prostate enlargement can interfere with ejaculation. Research on IVF outcomes shows that when a male partner is 40 or older and the female partner is between 35 and 39, live birth rates drop noticeably. Interestingly, a specialized fertilization technique called ICSI appears to correct for many of these age-related sperm defects, eliminating the impact of the man’s age on outcomes.
The bottom line: women’s fertility has a steeper, more time-sensitive decline, but men are not immune to age-related reproductive problems.
Lifestyle Factors That Affect Both Sexes
Several lifestyle factors reduce fertility across the board, though they sometimes work through different mechanisms in men and women.
- Weight: Obesity is linked to lower sperm count and quality in men. In women, excess weight worsens hormonal imbalances, particularly in those with PCOS. Losing just 5% of body weight significantly improves ovulation and pregnancy chances for women with PCOS. Being underweight disrupts ovarian function and can stop ovulation entirely.
- Smoking and substance use: Tobacco, marijuana, heavy alcohol use, and illegal drugs like heroin and cocaine reduce fertility in both men and women. Smoking damages egg quality in women and reduces sperm parameters in men.
- Stress and environment: Physical and psychological stress, along with occupational exposures to chemicals, heat, or radiation, can impair reproductive function in both sexes.
Secondary Infertility Is More Common Than You’d Think
Secondary infertility, the inability to conceive after a previous successful pregnancy, is actually more prevalent globally than primary infertility. Estimates place secondary infertility rates between 7% and 33% depending on the region, compared to 1% to 3% for primary infertility. This catches many couples off guard because they assume a prior pregnancy means future fertility is guaranteed.
Globally, secondary infertility prevalence is lower among men than women. Regional trends vary dramatically. Rates have been declining in Central Asia, Central and Eastern Europe, and high-income countries, but rising sharply in the Middle East, North Africa, and South Asia. These shifts likely reflect changes in infection rates, access to healthcare, and lifestyle patterns rather than any inherent biological change.
Why Both Partners Should Be Tested
Because male and female factors contribute to infertility at roughly equal rates, any fertility evaluation should include both partners from the start. For men, this means at least one semen analysis performed by a quality-controlled lab. For women, testing typically evaluates ovulation, fallopian tube patency, and uterine health. A full medical, reproductive, and sexual history from both partners is a standard first step.
The outdated assumption that infertility is primarily a female issue leads many couples to spend months or years investigating only one partner. Given that men contribute to nearly half of all infertility cases, testing both partners simultaneously saves time and leads to faster, more accurate diagnoses.