You've done everything right, yet you still aren't pregnant. You may be afraid that something is wrong -- after all, Cousin Emily and her husband managed to get pregnant on their first try. Is it you or is it your husband? Sex, that intimate experience you used to enjoy together, threatens to become a chore. I've heard women euphemistically refer to their menstrual period as their "friend," but now it has become your enemy. Each time it arrives you feel especially depressed.

Don't panic! There may not be anything wrong. Just because you've done everything you're supposed to doesn't mean you'll succeed immediately. Marge, who is 28, is typical of many patients who worry before they need to. When she came to see me, she was frantic. "We've tried everything for the past five months, but I'm still not pregnant. Let's do some tests!" I reassured her and suggested they keep trying, explaining that it was much too soon to begin any testing. And, as is usually the case, she returned several months later, her home pregnancy test having shown a positive result.

Even if both you and your partner are perfectly normal and destined to give birth to a healthy baby, it doesn't mean it will happen the first or second month that you try. Statistics tell us that, on the average, your chance of conceiving is only about 25 percent for each ovulatory cycle. Roughly translated, that means that the average couple takes four months to conceive. But that's average. Of normally fertile couples, one half will conceive by three months, 75 percent by six months, and 90 percent by one year.

If you've tried to become pregnant by having unprotected intercourse on a regular basis for one year without success, you're technically considered infertile (which is not at all the same thing as being sterile, a permanent condition). This occurs in 10-15 percent of couples, so you are certainly not alone.

Today, gynecologists are seeing more patients with infertility problems than in years past. This is partly due to the increase in sexually transmitted diseases (disease and infection can mess up your reproductive apparatus), and partly because many couples are postponing pregnancy until later in life, when fertility naturally decreases.

Being termed infertile doesn't mean that you will never become pregnant. In many infertile couples a treatable cause can be found. Think of it as a challenge that you have a reasonable chance of overcoming.

Annette, 32, consulted me after trying to conceive for only two months. Since she had a history of very irregular menses, with her period not arriving for months at a time, I didn't merely send her home to keep trying. Instead, I prescribed Clomid, a fertility drug, and soon Annette began having regular menses. Within a few months, she became pregnant.

A variety of factors affect how long it takes for any one woman to conceive. Age certainly plays a role. As you get older, it becomes harder to conceive. Also the type of birth control you were using may have an effect.

If you're not yet pregnant but think you should be, you might want to reevaluate your approach. Sex is necessary but not sufficient to become pregnant. Review your cycle lengths and identify your fertile time. Intercourse around the time of ovulation, not necessarily on the exact day, is required. Proper diet and rest are important, as is reducing the alcohol and tobacco consumption of both partners (smokers in some studies have been found to have impaired fertility). If you exercise strenuously, cutting back may be a good idea. Stress may also interfere with fertility. Although trying to relax is easier said than done, some people find that it helps to eliminate any avoidable stresses.

Unless you suffer from some obvious disorder, such as lack of menses, I usually recommend trying for a year before undergoing evaluation for infertility. However, if you're over 35, it's reasonable to ask for an infertility workup after six months of trying to conceive. After a year, you can consult either a gynecologist or a fertility specialist or center. A gynecologist is a specialist who, after completing medical school, spends four years in residency where he or she is trained to treat female medical problems, care for pregnant women, deliver babies, and treat infertility. She should be board-certified in obstetrics and gynecology. If your gynecologist is interested in and experienced with infertility, that may be a good place to start.

If your problem turns out to be complex or you don't respond to treatment, don't hesitate to consult a fertility specialist. Fertility or infertility specialists study reproductive endocrinology for two years after completing their residency. They should be board-certified in this subspecialty. They usually don't deliver babies or treat the majority of female problems, but rather specialize in female hormone irregularities and infertility.

Getting pregnant is a complicated physiological process, and many factors can interfere. In order for you to become pregnant, several steps must occur. Your partner must produce an adequate amount of normal active sperm, and they must be placed in the vagina at the right time. You must produce a healthy egg. The sperm must be able to swim up through the cervix and meet the egg, which has been picked up by the fallopian tube. Once the egg and sperm unite, they must be able to travel back to the uterine cavity and implant in a uterine lining that is developed properly for the event. Hormones must be produced appropriately in order for all this to occur. Any number of factors can go awry at almost any point in the process.

Approximately 10-15 percent of infertility cases are due to ovulation problems; 30-40 percent to such male factors as low sperm count or varicose veins in the testicles; 30-40 percent to pelvic disease; 10-15 percent to cervical problems; and about 5 percent to other, less common causes. Doctors are unable to find any cause in 5-10 percent of cases. Since more than one factor may contribute, one test alone, such as a blood test or a culture, often won't solve the mystery. Usually you will undergo a series of tests. About 90 percent of the time a cause is found, and usually, but not always, it's something correctable.

If you've already had a child or two, it's not unusual to have difficulty conceiving again. In fact, such secondary infertility is even more common than primary infertility. Many of the same factors may be involved, with increasing age being one of the most significant. As a woman ages, she has more chance of developing medical problems -- endometriosis or a pelvic infection, for example -- that may eventually interfere with fertility. Also, as a man ages, the number and quality of his sperm may be affected by such factors as disease and exposure to pollutants.