What Is Infertility? Definitions, How Common It Is, and When to Seek Help

Infertility is common, and it affects men and women. This guide explains how health authorities define it, how often it occurs, and what US fertility clinic data shows about the reasons people turn to IVF. It describes information, not a diagnosis. Only a clinician who knows your history can assess your situation.

How infertility is defined

The World Health Organization defines infertility as a disease of the male or female reproductive system, defined by the failure to achieve a pregnancy after 12 months or more of regular unprotected sexual intercourse.^[1] It can be due to male factors, female factors, or unexplained factors.^[1]

The US National Institute of Child Health and Human Development (NICHD) uses a similar definition. It adds an age adjustment: infertility describes a couple unable to achieve pregnancy after 1 year of regular, unprotected sex, or after 6 months if the woman is older than 35.^[2] NICHD also notes that the term is used for women who can get pregnant but cannot carry a pregnancy to term because of miscarriage.^[2]

Infertility vs. subfertility

NICHD distinguishes infertility from subfertility. Subfertility means pregnancy is likely to happen without medical help, but it takes longer than usual.^[2]

Primary and secondary infertility

MedlinePlus describes two types:^[3]

• Primary infertility: couples who have not become pregnant after at least 1 year of sex without birth control.
• Secondary infertility: couples who have been pregnant at least once but are now unable to become pregnant.

How common is infertility?

The WHO estimates that approximately one in every six people of reproductive age worldwide experience infertility at some point in their lifetime.^[1] It describes infertility as affecting millions of people and their families and communities.^[1]

Is it a “female” or a “male” problem?

Both. NICHD states that problems in the male are just as likely as problems in the female, and that the cause can be a combination of both partners.^[4] It reports that men are the only cause or a contributing cause in about 40% of couples’ infertility problems.^[4] In many cases, no exact cause is found. This is called unexplained or idiopathic infertility.^[4]

For a closer look at specific conditions, see causes of infertility in women and men and male infertility and ICSI.

Age and fertility

Age is one of the most important factors. MedlinePlus states that healthy couples under 30 who have sex regularly have about a 20% chance of getting pregnant each month.^[3] It adds that a woman’s chance of getting pregnant begins to decrease around age 35, especially after 40, although the age when fertility starts to decline varies from woman to woman.^[3]

The same pattern shows up in IVF outcomes. In 2022, the share of intended egg retrievals resulting in a live birth was 49.7% for patients under 35 using their own eggs, versus 7.7% for patients over 40.^[6] See IVF success rates by age.

When do people seek an evaluation?

MedlinePlus says health care providers suggest that women under 30 try to get pregnant on their own for 1 year before testing, and that women over 35 try for 6 months before talking to their provider.^[3] This matches the age-adjusted NICHD definition above.^[2] Testing usually involves both partners. See fertility testing: what to expect.

People also see fertility specialists for reasons other than infertility, such as freezing eggs or embryos for the future, single parenthood, same-sex couples building a family, or avoiding passing on a genetic condition.

Why people use IVF: what the US data shows

US fertility clinics report to the CDC the reasons for using assisted reproductive technology (ART). More than one reason can be recorded, so the shares below add up to well over 100%.^[6]

Reason for using ART (CDC category)	National share, 2022
Egg or embryo banking	43%
Male factor	28%
Diminished ovarian reserve	26%
Other reason, infertility	26%
Preimplantation genetic testing	18%
Ovulatory dysfunction	14%
Unexplained infertility	11%
Tubal factor	10%
Recurrent pregnancy loss	7%
Other reason, non-infertility	7%
Endometriosis	6%
Uterine factor	6%
Gestational carrier	2%

Two things stand out.^[6] First, egg or embryo banking is the most frequently reported reason (43%). That reflects people freezing eggs or embryos for later use, which is not always related to infertility. Second, male factor (28%) and diminished ovarian reserve (26%) are the most common infertility diagnoses in the data. The CDC defines diminished ovarian reserve as a reduced ability of the ovary to produce eggs, and male factor infertility as low sperm count or problems with sperm function.^[7]

How infertility is treated

Treatment depends on the cause. NICHD notes that treatments range from medication to assisted reproductive technology, and that in 85% to 90% of cases infertility is treated with conventional medical therapies such as medication or surgery.^[5] If treatments are unsuccessful, eggs or sperm from a donor, or a gestational carrier, are other options.^[5]

IVF is the most common type of ART.^[7] For how IVF compares with less intensive treatment, see IUI vs. IVF. To find clinics near you, browse US fertility clinics by state.

Emotional support

Infertility evaluation and treatment can be stressful. MedlinePlus notes that support groups can help.^[3] Many fertility clinics also offer counseling or can refer you to a mental health professional with experience in fertility.

Key takeaways

• Infertility is usually defined as not achieving pregnancy after 12 months of regular unprotected sex, or 6 months if the woman is over 35.^[1][2]
• About one in six people of reproductive age worldwide experience it.^[1]
• Male and female factors are about equally likely, and causes are often combined or unexplained.^[4]
• Most infertility is treated without IVF; IVF and other ART are options when other treatments do not work or are not suitable.^[5]