The medical term for not being able to have kids is infertility. It’s defined as the failure to achieve pregnancy after 12 months of regular, unprotected sex. About 1 in 8 women of reproductive age in the U.S. are affected. But “infertility” is actually one of several related terms, and the differences between them matter depending on your situation.
Infertility, Sterility, and Subfertility
These three words get used loosely in everyday conversation, but they mean different things in medicine. Infertility refers to not conceiving after a year of trying. It doesn’t necessarily mean pregnancy is impossible. Many people diagnosed with infertility go on to conceive with treatment or even on their own.
Sterility is more absolute. It means the body cannot produce a pregnancy at all, such as when someone has had their uterus or both ovaries removed, or when a person produces no sperm. Sterility is permanent without intervention like surrogacy or donor gametes.
Subfertility sits between the two. It describes reduced fertility where conception takes longer than expected but isn’t ruled out. Someone with subfertility might eventually conceive without help, just over a longer timeline. In practice, doctors often use “infertility” and “subfertility” interchangeably, though subfertility more accurately captures the idea that fertility exists on a spectrum.
Primary vs. Secondary Infertility
If you’ve never been pregnant, the diagnosis is called primary infertility. If you’ve had at least one pregnancy before (even if it didn’t result in a live birth) but can’t conceive again, that’s secondary infertility. Secondary infertility is surprisingly common and can be confusing for people who assumed that having one child meant they’d have no trouble having another. CDC data shows that about 6% of married women who already have at least one child meet the criteria for infertility, compared to roughly 19% of married women who have never given birth.
Common Causes in Women
Ovulation problems are the most frequent cause of female infertility. Polycystic ovary syndrome (PCOS) is one of the biggest culprits, affecting up to 20% of women during their reproductive years. PCOS disrupts the normal release of eggs and is often accompanied by irregular periods, excess body hair, and insulin resistance.
Endometriosis is another major cause, affecting roughly 10% of reproductive-age women. In this condition, tissue similar to the uterine lining grows outside the uterus, typically on the ovaries, fallopian tubes, or pelvic cavity. This misplaced tissue causes inflammation that can damage eggs, block tubes, or interfere with implantation.
Premature ovarian insufficiency, sometimes called early menopause, occurs when the ovaries stop functioning normally before age 40. Blocked or damaged fallopian tubes, uterine abnormalities, and hormonal imbalances round out the other common causes.
Common Causes in Men
Male factors contribute to roughly half of all infertility cases, either alone or in combination with female factors. The most common issue is low sperm count, medically called oligospermia. A complete absence of sperm in the semen is called azoospermia.
One of the most treatable causes of male infertility is a varicocele, which is a swelling of the veins that drain the testicle. Varicoceles raise the temperature around the testicles, which can lower both sperm count and sperm quality. Other causes include hormonal imbalances, blockages in the reproductive tract, genetic conditions, and lifestyle factors like excessive heat exposure or certain medications.
Unexplained Infertility
Sometimes all the standard tests come back normal for both partners, yet pregnancy still doesn’t happen. This is called unexplained infertility, and it accounts for a significant portion of cases. The diagnosis essentially means that current testing can’t pinpoint a specific cause, not that nothing is wrong. There may be subtle issues with egg quality, sperm function, or implantation that existing tests aren’t sensitive enough to detect. Unexplained infertility can still respond well to treatment.
How Age Affects Fertility
Age is the single strongest predictor of fertility, particularly for women. Egg quantity and quality decline gradually starting in the early 30s and then drop more sharply after 35. Birth rate data illustrates this clearly: in 2023, there were about 94 births per 1,000 women aged 30 to 34, but only 54 per 1,000 for women aged 35 to 39, and just 12.5 per 1,000 for women aged 40 to 44.
This decline is why medical guidelines adjust the timeline for seeking help based on age. The American Society for Reproductive Medicine recommends evaluation after 12 months of trying for women under 35, after 6 months for women 35 and older, and more immediately for women over 40. If you have a known medical condition linked to infertility, such as PCOS or endometriosis, evaluation can start right away regardless of age. Male fertility also declines with age, though more gradually and with less predictable cutoffs.
What an Evaluation Looks Like
A fertility evaluation typically involves both partners. For women, it usually starts with blood tests to check hormone levels and assess ovarian reserve (how many eggs remain), along with imaging to look at the uterus and fallopian tubes. For men, the primary test is a semen analysis, which measures sperm count, movement, and shape. These initial tests can often identify or rule out the most common causes within a few weeks.
If you’ve been searching for the right word to describe what you’re going through, “infertility” is the term that opens the door to evaluation, treatment options, and insurance coverage where available. It’s a medical diagnosis, not a permanent label, and for many people it’s a starting point rather than a final answer.