In the United States, around 15% of women ages 15 to 44 years (around 6 million) have trouble getting pregnant or carrying a baby to term. Infertility is a failure for a couple to achieve conception after one year of regular, unprotected intercourse. There are many risk factors for infertility, as well as separate causes of the condition.

Risk Factors

Risk factors for female infertility are different than causes. Just because a woman has a risk factor does not mean she is infertile. A risk factor just puts her at higher risk of having infertility than someone who does not possess the risk factor. Risk factors for female infertility include:

  • Advanced age – Fertility begins to decline when a woman reaches the mid-30s, and after late-30s, it rapidly declines. In addition, quality of eggs declines with age, which puts a woman at risk for spontaneous abortion or having a child with birth defects.
  • Weight – Being underweight or overweight are risk factors for infertility. Women’s estrogen is 30% produced by fat cells. When there is an abnormal level of estrogen, pregnancy is affected. Obesity is related to PCOS, as well as hormone imbalances.
  • Smoking – Along with causing other health problems, smoking increases a person’s chances of being infertile.

Ovulation Problems

Ovulation is the release of an egg, and it occurs during the monthly cycle (between days 10 and 18). Problems that affect hormones and ovulation are the most common causes of female infertility. These include:

  • Polycystic ovarian syndrome (PCOS) – Women with this condition do not ovulate regularly or at all. The ovaries produce too many androgens, which are male hormones. Increased androgen production affects levels of reproductive hormones, and tiny cysts form on the ovaries.
  • Premature ovarian failure – Called early menopause, premature ovarian failure is the depletion of ovary follicles before age 40. This is caused by hormone problems, genetic disorders (Turner’s syndrome), or autoimmune issues (systemic lupus erythematosus, type 1 diabetes, Addison’s disease).

Blocked Fallopian Tubes

A blocked fallopian tube will prevent sperm from reaching the egg to fertilize it. Blockage of one or both tubes also can prevent a fertilized egg from reaching the uterus to implant there. Conditions that can lead to fallopian tube blockage include:

  • Endometriosis – With this condition, the cells that line the uterus grow in areas outside the uterus (abdomen, intestines, ovaries). The condition can lead to pain and reduce fertility. Severe scar tissue can form and cause blockage of the fallopian tubes.
  • Pelvic inflammatory disease (PID) – This condition is caused by repeated infections of the reproductive tract. Common causes are sexually transmitted diseases. PID leads to scar tissue formation outside the uterus, as well as near the cervix.
  • Adhesions – Uterine and abnormal scarring can occur from pelvic surgery or infection. These bands of scar tissue can restrict movement of the ovaries and fallopian tubes, causing infertility.

Other Causes of Infertility

Several other problems can lead to female infertility. Other causes include:

  • Elevated prolactin levels – Prolactin is a hormone that stimulates breast development. High levels of this hormone will reduce reproductive hormones and inhibit ovulation. Elevated prolactin levels can be related to underactive thyroid glands, pituitary adenomas, and other growths of the glands/brain.
  • Congenital structural abnormalities – Congenital reproductive tract abnormalities may cause infertility. Anything that results in structural abnormalities of the fallopian tubes or uterus can affect sperm reaching the egg, as well as egg implantation into the uterine lining.

Cervical mucus abnormalities – Low amounts of cervical mucus, or poor quality cervical mucus, can lead to infertility. This problem is related to prior surgery, hormonal imbalances, and certain medications.