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To become pregnant, the complex processes of ovulation and fertilization need to work just right. For some couples, infertility problems can be present from birth (congenital) or something can go wrong along the way that results in infertility.

The reasons for infertility can involve one or both partners. In general:

  • In about one-third of cases, the cause of infertility involves only the male.
  • In about one-third of cases, the cause of infertility involves only the female.
  • In the remaining cases, the cause of infertility involves both the male and female, or no cause can be identified.

Causes of male infertility

Causes of male infertility may include:

  • Abnormal sperm production or function due to various problems, such as undescended testicles, genetic defects, health problems such as diabetes, or infections such as mumps. Enlarged veins in the testes (varicocele) can increase blood flow and heat, affecting the number and shape of sperm.
  • Problems with the delivery of sperm due to sexual problems, such as premature ejaculation; semen entering the bladder instead of emerging through the penis during orgasm (retrograde ejaculation); certain genetic diseases, such as cystic fibrosis; structural problems, such as blockage of the part of the testicle that contains sperm (epididymis); or damage or injury to the reproductive organs.
  • Overexposure to certain environmental factors, such as pesticides and other chemicals, radiation, or to certain medications, such as anabolic steroids, or marijuana. In addition, frequent exposure to heat, such as in saunas or hot tubs, can elevate core body temperature, impairing sperm production.
  • Damage related to cancer and its treatment, including radiation or chemotherapy. Treatment for cancer can impair sperm production, sometimes severely. Removal of one testicle due to cancer also may affect male fertility.

Causes of female infertility

Causes of female infertility may include:

  • Ovulation disorders, which hinder or prevent the ovaries from releasing eggs. Examples include hormonal disorders such as polycystic ovary syndrome, a condition that might relate to your ovaries producing too much of the male hormone testosterone, and hyperprolactinemia, when you have too much prolactin — the hormone that stimulates breast milk production. Other underlying causes may include excessive exercise, eating disorders, injury or tumors.
  • Uterine or cervical abnormalities, including problems with the opening of the cervix or cervical mucus, or abnormalities in the shape or cavity of the uterus. Benign tumors in the wall of the uterus that are common in women (uterine fibroids) may rarely cause infertility by blocking the fallopian tubes. More often, fibroids may distort the uterine cavity interfering with implantation of the fertilized egg.
  • Fallopian tube damage or blockage, which usually results from inflammation of the fallopian tube (salpingitis). This can result from pelvic inflammatory disease, usually caused by sexually transmitted infection, endometriosis or adhesions.
  • Endometriosis, which occurs when endometrial tissue implants and grows outside of the uterus — often affecting the function of the ovaries, uterus and fallopian tubes.
  • Primary ovarian insufficiency, also called early menopause, when the ovaries stop working and menstruation ends before age 40. Although the cause is often unknown, certain conditions are associated with early menopause, including immune system diseases, radiation or chemotherapy treatment, and smoking.
  • Pelvic adhesions, bands of scar tissue that bind organs after pelvic infection, appendicitis, or abdominal or pelvic surgery.

Other causes in women include:

  • Thyroid problems. Disorders of the thyroid gland, either too much thyroid hormone (hyperthyroidism) or too little (hypothyroidism), can interrupt the menstrual cycle or cause infertility.
  • Cancer and its treatment. Certain cancers — particularly female reproductive cancers — often severely impair female fertility. Both radiation and chemotherapy may affect a woman's ability to reproduce.
  • Other conditions. Medical conditions associated with delayed puberty or the absence of menstruation (amenorrhea), such as celiac disease, Cushing's disease, sickle cell disease, kidney disease or diabetes, can affect a woman's fertility. Also genetic abnormalities can make conception and pregnancy less likely.
  • Certain medications. Temporary infertility may occur with the use of certain medications. In most cases, fertility is restored when the medication is stopped.
Jul. 19, 2013