What Is Infertility?

Infertility is the inability to produce children. Although often the woman is blamed, infertility occurs in both men and women. On average, infertility affects 1 of every 10 couples. A couple is considered infertile after having 12 months of unprotected sex without pregnancy. A couple can be infertile whether or not the woman has been pregnant in the past.

Among couples with no fertility problems, 85% of women will become pregnant over one year. On average, pregnancy occurs after 3 to 6 months of unprotected sex. There is great variation around this average, however.

Pregnancy wastage is another form of infertility: A woman can become pregnant, but miscarriage or stillbirth prevents a live birth.

What Causes Infertility?

Different factors or conditions can reduce fertility, such as:

  • Infectious diseases (sexually transmitted infections [STIs], including HIV, other reproductive tract infections; mumps that develop after puberty in men)
  • Anatomical, endocrine, genetic, or immune system problems
  • Aging
  • Medical procedures that bring infection into a woman's upper reproductive tract

STIs are a major cause of infertility. Left untreated, gonorrhea and chlamydia can infect fallopian tubes, the uterus, and ovaries. 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. Men can have scarring and blockage in the sperm duct (epididymis) and urethra from untreated gonorrhea and chlamydia (see Female Anatomy, and Male Anatomy).

Other reasons for male infertility include a natural inability either to produce any sperm at all or enough sperm to cause pregnancy. Less commonly, sperm are malformed and die before reaching an egg. Among women, natural inability to become pregnant often is due to blocked fallopian tubes or inability to ovulate.

Fertility is also related to age. As a woman gets older, her ability to become pregnant naturally deceases over time. Emerging evidence suggests that, similarly, men, as they age, produce sperm that is less able to fertilize an egg.

Postpartum and postabortion infections also can cause PID, which may lead to infertility. This happens when the surgical instruments used for medical procedures are not properly disinfected or sterilized. A woman can also develop PID if an infection present in the lower reproductive tract is carried into the upper reproductive tract during a medical procedure.

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