About 1 in 6 people worldwide experience infertility, according to a 2023 World Health Organization report. That translates to roughly 17.5% of the adult population globally. The number is strikingly consistent across economic lines: 17.8% in high-income countries and 16.5% in low- and middle-income countries.
How Infertility Is Defined
Clinically, infertility means not achieving pregnancy after one year of regular, unprotected sex. If the woman is over 35, that window shortens to six months. These aren’t arbitrary cutoffs. They reflect the point at which natural conception becomes statistically unlikely without some form of medical evaluation or intervention.
It’s worth noting that the 1-in-6 figure from the WHO captures lifetime prevalence, meaning people who experienced infertility at any point in their reproductive years, not just those struggling right now. Some of those people eventually conceived on their own or with treatment. Others did not.
Infertility in the United States
U.S. data from the CDC’s National Survey of Family Growth (2015-2019) breaks things down differently than the global numbers, focusing specifically on women of reproductive age. Among all women ages 15 to 49, 13.4% have what the CDC calls “impaired fecundity,” a broader category that includes difficulty getting pregnant or carrying a pregnancy to term. Among married women in the same age range, that number rises to 16.3%.
The percentage of married women ages 15 to 49 who meet the strict clinical definition of infertility is 8.5%. That lower number reflects the narrower criteria: specifically the inability to conceive after a year of trying, rather than the wider umbrella of reproductive difficulties.
Roughly 13.7% of U.S. women ages 20 to 49 have used some form of fertility services at some point. That includes everything from basic testing and ovulation-stimulating medications to more intensive procedures like IVF.
Male Infertility Is More Common Than People Think
A persistent misconception is that infertility is primarily a female issue. The data tells a different story. A male factor is the sole cause in about 30% of couples struggling to conceive. In another 20% of cases, both male and female factors contribute. That means half of all infertility cases involve a problem on the male side.
There’s also growing concern about long-term trends in male reproductive health. A widely cited 1992 meta-analysis found that average sperm concentrations dropped from 113 million sperm per milliliter to 66 million between 1940 and 1990, while average semen volume fell from 3.4 to 2.75 milliliters over the same period. The causes behind this decline remain debated, with environmental chemicals, obesity, heat exposure, and lifestyle factors all under investigation.
What Causes Infertility
In women, the most common causes involve problems with ovulation, meaning the ovaries don’t release eggs regularly or at all. Conditions like polycystic ovary syndrome (PCOS) and diminished ovarian reserve (fewer remaining eggs, which happens naturally with age) account for a large share of cases. Blocked or damaged fallopian tubes, often from past infections or endometriosis, are another frequent cause.
In men, infertility typically comes down to sperm: too few, poor motility (they don’t swim well), or abnormal shape. Varicoceles, which are enlarged veins in the scrotum that raise testicular temperature, are the most common treatable cause of male infertility. Hormonal imbalances, genetic conditions, and prior infections can also play a role.
In roughly 10 to 15% of cases, no clear cause is found in either partner. This is classified as unexplained infertility, which can be one of the more frustrating diagnoses to receive because there’s no obvious target for treatment.
Age Is the Single Biggest Factor
Fertility declines with age in both sexes, but the effect is more dramatic and time-sensitive in women. A woman’s fertility begins declining gradually in her early 30s and drops more sharply after 35, which is why the clinical threshold for evaluation shortens from 12 months to 6 months at that age. By 40, the chance of conceiving naturally in any given cycle is significantly lower than at 30, and the risk of miscarriage rises substantially.
Male fertility also declines with age, though more gradually. Sperm quality, including concentration, motility, and genetic integrity, tends to decrease after age 40. Older paternal age is also associated with longer time to conception and a modestly higher risk of certain developmental conditions in offspring.
The Gap Between Prevalence and Treatment
Despite infertility affecting nearly 1 in 6 adults globally, access to treatment varies enormously. In the United States, fertility services can cost tens of thousands of dollars, and insurance coverage is inconsistent. Only a subset of states mandate any level of fertility treatment coverage. In low- and middle-income countries, where the WHO data shows infertility rates are nearly as high as in wealthy nations, advanced treatments like IVF are often completely out of reach.
This means the true burden of infertility is likely larger than treatment statistics suggest. Many people who would benefit from evaluation or intervention never access it, whether due to cost, stigma, or lack of available care. The 13.7% of U.S. women who have used fertility services represents only those who were able to seek help, not everyone who needed it.