Infertility is medically defined as the inability to become pregnant after 12 months of regular sexual intercourse without birth control or, for women over age 35, six months. Infertility also refers to women who are unable to carry a pregnancy to term. The Centers for Disease Control and Prevention (CDC) estimates that about one in eight U.S. women of childbearing age has difficulty getting pregnant or staying pregnant.
What Causes Infertility?
For pregnancy to occur, many complex processes and factors need to line up. A woman must produce a healthy egg; a man must produce healthy sperm. Favorable cervical fluid needs to be present so that sperm travel from the vagina to meet the egg while it’s still in the fallopian tube. Timing of intercourse or insemination is critical, since an egg generally lives only 24 hours. Once the sperm and egg join, this single cell divides to become an embryo, which must implant properly in the uterine lining before it can grow. Couples can experience infertility when there is a problem with any one or more of these delicate phases of conception.
Why a Woman May Experience Infertility
Age is the most important factor affecting a woman’s fertility. (For more information, see Fertility and Aging.) Long before menopause, our bodies’ reproductive capabilities slow down. This natural decline of fertility happens in all women, though it happens at different ages for individual women.
I am 39 years old; finally, my life is settled enough to start having a family . . . the doctor did a blood test and told me even though I had regular menstrual periods, my ovarian function was poor, I was premenopausal, and my chances of getting pregnant and not miscarrying were low.
Though women can experience other causes of infertility at any age, infertility among older women is often the result of normal age-related changes occurring in the reproductive hormones that make a woman’s ovaries less able to release eggs, decrease the number of healthy eggs she has left, and increase her risk of miscarriage.
Overall, one of the most common causes of female infertility is linked to problems with ovulation, the physiological process by which eggs mature. An important sign that a woman is not ovulating normally is irregular or absent menstrual periods. However, a woman can be having regular periods and still have problems with ovulation. One cause of ovulation problems is polycystic ovarian syndrome (PCOS), a metabolic disorder affecting nearly 10 percent of all women, that can interfere with hormone production and ovulation.
Premature ovarian insufficiency (POI) is also linked to ovulation problems and occurs when a woman’s ovaries stop functioning fully before the age of forty. POI, which affects about 1 percent of all women, is not the same as early menopause.
Ovulation problems may also be due to thyroid disorders, adrenal gland disorders, benign pituitary tumors, excessive exercise, diabetes, weight loss, obesity, or medications such as for cancer treatments.
Another common cause of infertility is blocked fallopian tubes or other structural problems. This can be due to endometriosis, pelvic inflammatory disease (PID), or scarring due to surgery or repeated injury. Some women are born with structural abnormalities affecting their reproductive organs that may also prevent the egg from traveling down the fallopian tube, inhibit the growing embryo from implanting in the uterus, or increase the risk of an ectopic pregnancy. Uterine fibroids, which are noncancerous growths in the uterus, are also associated with obstructions in the uterus and/or fallopian tubes as well as repeated miscarriages. Other possible causes of infertility include immune system problems, issues with the cervical fluid, and luteal phase defects.
Why a Man May Experience Infertility
Sometimes a man is born with a condition that causes male infertility and other times problems emerge later in life due to illness or injury. More than 90 percent of male infertility is due to sperm abnormalities affecting sperm count, sperm motility (movement), or sperm morphology (shape). Some causes of male infertility include:
- Varicocele, which occurs when the enlarged veins on a man’s testicle(s) cause temperature increases that can affect the number or shape of the sperm.
- Retrograde ejaculation, which occurs when the muscles of the bladder wall do not function properly and sperm are forced backward into the bladder instead of forward out the urethra. This can be caused by surgery, spinal cord injury, certain medications, or aging.
- Structural abnormalities that damage or block testes, the ducts that carry the mature sperm, or other reproductive structures.
- Underdeveloped, undescended, or injured testes.
Sometimes, even after extensive testing, physicians are unable to find any medical reason for the infertility. You seem to be ovulating normally, your fallopian tubes are open and healthy, your partner has a high sperm count with good motility, and neither of you has any other underlying health issues. This type of diagnosis provides hope to some—maybe, if there is no known problem, pregnancy will happen after all—while it leaves others extremely frustrated—if we don’t even know what’s causing the problem, how can we address it?