Fertility refers to the ability to conceive and carry a child to birth. Infertility is a disease of the reproductive system that impacts that ability. It's far more common than most people realize, with about 10 percent of the reproductive age population affected by infertility. When there is no pregnancy after twelve or more months of unprotected sex, the diagnosis is infertility. Couples who have never had a child, are said to have primary infertility. Those who have become pregnant at least once but are unable to conceive again are said to have secondary infertility.

Though the human body is designed to bear children, the process of conception and pregnancy is complex and depends upon many factors. Fertility requires healthy sperm and eggs, unblocked fallopian tubes that allow the sperm and eggs to meet, and the sperm's ability to fertilize the egg. Then the fertilized egg must be able to implant in the uterus and grow into a healthy embryo/fetus in an environment that supports its development. A problem with any one of these factors can lead to impaired fertility - difficulty conceiving or carrying a child to term.

Even when all conditions are perfect, pregnancy is never guaranteed. Fecundabilty is the monthly probability of conception. Even in conditions of optimum fertility, the chances of getting pregnant are only 20 - 25 percent per month. About 72 percent of couples will conceive within six months, and 85 percent within a year. Fecundabilty rates begin to decrease once the woman turns 30, with rates dropping again at 35 and 40.

While the general guideline is to see a doctor to discuss fertility after one year of unprotected sex (two-three times/week) without conception, women over age 35 have less time left in which to bear a child and so should seek assistance after six months. Other conditions that justify seeing a doctor sooner are periods at three week (or less) intervals, no period for more than three months, irregular periods, a history of pelvic infections, two or more miscarriages, men who have had prostate infections, and men whose testes are not felt in the scrotum.

Couples who are concerned about their fertility should talk first with their primary care physician or the woman's gynecologist. Some problems can be dealt with quite easily at this level of care. If necessary, the primary care/gyn can refer you to a fertility specialist.