How Is Infertility Defined, and How Common Is It?

What does infertility mean clinically?

Infertility is clinically defined as not being able to achieve pregnancy after 1 year of having regular, unprotected intercourse. For women older than 35, the clinical definition is not being able to achieve pregnancy after 6 months of regular, unprotected intercourse NICHD. That timing matters because age can change how long it makes sense to wait before getting evaluated.

The term also covers more than trouble getting pregnant in the first place. It can describe a couple’s inability to get pregnant, or a woman’s inability to carry a pregnancy to term NICHD. In plain language, infertility is not a single experience with one cause or one pattern.

How common is infertility in the United States?

Infertility and related fertility problems affect a substantial number of adults in the U.S. The National Institute of Child Health and Human Development says about 9% of men and about 11% of women of reproductive age in the United States have experienced fertility problems NICHD. Those figures are broad national estimates, so they do not describe one person’s situation, but they do show that fertility problems are not rare.

CDC data add another useful perspective by reporting measures of impaired fecundity and infertility among women ages 15–49. In 2015–2019, 13.4% of women ages 15–49 had impaired fecundity, and 8.5% of married women ages 15–49 were infertile CDC. The CDC also reports that 16.3% of married women ages 15–49 had impaired fecundity CDC. These numbers are not the same as the NICHD estimate because they measure different groups and different outcomes.

What is the difference between infertility and impaired fecundity?

Infertility and impaired fecundity are related but not identical terms. The CDC uses impaired fecundity to describe difficulty getting pregnant or carrying a pregnancy, while infertility is a narrower measure reported for married women ages 15–49 CDC. That is why the CDC reports a higher percentage for impaired fecundity than for infertility.

This distinction helps explain why prevalence numbers can look different depending on the source. A person may be counted in one measure and not the other because the definitions, age ranges, and marital status categories are not the same CDC. When reading fertility statistics, it helps to look closely at what is being measured before comparing numbers.

Why does the definition use 1 year, or 6 months after age 35?

The standard clinical definition uses time because pregnancy does not always happen right away, even when conception is possible. Waiting 1 year of regular, unprotected intercourse before defining infertility gives many couples time to try without labeling a temporary delay as a medical problem NICHD. For women older than 35, the time frame shortens to 6 months because age is an important factor in fertility NICHD.

That definition is about when infertility is identified clinically, not about predicting whether pregnancy can or cannot happen in the future. Many different medical conditions and other factors can contribute to fertility problems, and a case may have one cause, several causes, or no identifiable cause NICHD. In other words, the diagnosis is a starting point for looking for reasons, not a complete explanation by itself.

What else do national data show about fertility problems?

CDC data show that fertility-related concerns are common enough that many women have used fertility services at some point. Among women ages 20–49 in the United States, 13.7% had ever used fertility services in 2022–2023 CDC. That statistic does not tell us why they used services, but it does show that fertility care is part of the experience for many families.

The CDC also breaks down data by parity, meaning whether a woman has had births before. Among women ages 15–49, impaired fecundity was 13.8% for those with no births and 13.1% for those with one or more births CDC. For married women ages 15–49, impaired fecundity was 26.0% among those with no births and 14.1% among those with one or more births CDC. Those differences show that fertility problems can affect people at different points in family-building.

What should you make of these statistics?

The most helpful way to read infertility statistics is to treat them as population-level estimates, not personal forecasts. A national percentage tells us how common a condition is in a defined group, but it does not explain the cause for one individual or couple CDC. It also does not tell you how long treatment might take or what outcome to expect.

It is also important to remember that data sources may use different definitions. NICHD describes infertility clinically as 1 year of regular, unprotected intercourse without pregnancy, or 6 months for women older than 35 NICHD. The CDC reports both impaired fecundity and infertility in selected U.S. groups, which is useful for understanding the broader picture but not always directly comparable to other estimates CDC. When numbers differ, the difference is often about measurement, not contradiction.

Why does this definition matter for family-building?

A clear definition helps people know when fertility challenges have crossed from “still trying” into a medical issue worth evaluating. That does not mean every person needs the same next step, but it does mean the timeline is not arbitrary NICHD. For many people, understanding the clinical definition can make it easier to decide when to ask questions and gather information.

It can also reduce confusion when reading articles, insurance materials, or statistics. Some sources focus on infertility, while others use impaired fecundity or other fertility measures CDC. Knowing which term is being used makes the data easier to interpret and keeps the discussion grounded in the same medical language.

Bottom line

Infertility is clinically defined as not achieving pregnancy after 1 year of regular, unprotected intercourse, or after 6 months for women older than 35 NICHD. National data show that fertility problems affect many adults in the United States, with about 9% of men and 11% of women of reproductive age reporting fertility problems, and CDC estimates showing 13.4% of women ages 15–49 with impaired fecundity and 8.5% of married women ages 15–49 classified as infertile NICHD CDC. The exact number depends on the definition being used, but the broader message is consistent: fertility problems are common, and the clinical definition gives them a clear starting point.