What Is Infertility?

Involuntary infertility is a disease of the reproductive system: the inability to become pregnant when desired. Involuntary childlessness is the inability to give birth to desired children, whether due to inability to achieve pregnancy or due to stillbirth or miscarriage. These conditions occur in couples who have never had children (primary infertility) and, more often, in couples who have had children previously (secondary infertility). Infertility is “defined by the failure to establish a clinical pregnancy after 12 months of regular unprotected sexual intercourse” between a man and a woman. (On average, 85% of women would be pregnant by then.)

Worldwide, infertility affects about 12% of couples who are seeking to have a child—about 2% who have never had children and about 10% who have had children previously. There are differences among regions.

In some countries or communities, infertility or childlessness can have drastic consequences, especially for women but also with significant impact on men. These consequences can include economic deprivation, divorce, stigma and discrimination, isolation, intimate partner violence, murder, mental health disorders, and suicide.

What Causes Infertility?

Globally, infertility has many causes, which vary depending on the setting. Although often the woman is blamed, the cause of infertility can be in either the man or the woman or in both.

Medically, causes of infertility range from the effects of sexually transmitted infections (STIs) in one or both partners to hormonal imbalances and defects of the uterus in women and low sperm count, low sperm motility, and malformed sperm in men. Lifestyle factors include smoking, alcohol, and drug abuse as well as obesity and nutritional deficiencies. Exposures to chemicals in the environment that disrupt the endocrine system as well as other environmental and stress-related factors are suspected as well.

A large WHO study in the late 1970s found that STIs were a major cause of infertility in developing countries. It is not known how much STIs contribute to infertility now.

However, the evidence is clear that, if left untreated, gonorrhea and chlamydia can infect the fallopian tubes, the uterus, and the ovaries in women. This is known as pelvic inflammatory disease (PID). Clinical PID is painful, but sometimes PID has no symptoms and goes unnoticed (silent PID). Gonorrhea and chlamydia can scar women’s fallopian tubes, blocking eggs from traveling down the tubes to meet sperm. Similarly, untreated gonorrhea and chlamydia in men can cause scarring and blockage in the sperm duct (epididymis) and urethra (see Female Anatomy, and Male Anatomy).

Other factors or conditions that can reduce fertility or cause infertility include:

  • Other reproductive tract infections, including genital tuberculosis (TB) in both men and women
  • HIV
  • Medical procedures that introduce infection into a woman’s upper reproductive tract or uterus, including postpartum and postabortion infections
  • Mumps that develop after puberty in men
  • Certain disorders of the reproductive tract, such as endometriosis, polycystic ovaries, and fibroids (myomas)
  • Anatomical, endocrine, genetic, or immune system problems in both men and women
  • Surgical interventions that adversely affect reproductive tissues or organs
  • Cancer treatments that affect reproductive health and the capacity to reproduce
  • Aging in both women and men