Conception requires the juxtaposition of the male and female gametes at the optimal stage of maturation, followed by transportation of the conceptus to the uterine cavity at a time when the endometrium is supportive of its continued development and implantation (see Chapter 4). For these events to occur, the male and female reproductive systems must be both anatomically and physiologically intact, and coitus must occur with sufficient frequency and at the proper time (preferably a few hours before) to the release of the oocyte from the follicle. Even when fertilization occurs, it is estimated that more than 70% of resulting embryos are abnormal and fail to develop or become nonviable shortly after implantation.

Considering the vast complexity of the reproductive process, it is remarkable that 80% of couples achieve conception within 1 year. More precisely, 25% conceive within the first month, 60% within 6 months, 75% by 9 months, and 90% by 18 months. The steadily decreasing rate of monthly conception demonstrated by these figures most likely reflects a spectrum of fertility extending from highly fertile couples to those with relative infertility. After 18 months of unprotected sexual intercourse, the remaining couples have a low monthly conception rate without treatment, and many may have absolute defects preventing fertility (sterility).

Conception requires adequate function of multiple physiologic systems in both partners. Infertility may result from either one major deficiency (e.g., tubal occlusion) or multiple minor deficiencies. Failure to realize this important dictum may lead the inexperienced practitioner to overlook additional factors that might be more amenable to treatment than the one that has been identified. Infertility in about 40% of infertile couples has multiple causes. Therefore, in general, a complete infertility evaluation should be performed on each couple.

Age substantially decreases the rate of conception because of lower embryo quality, reduced ovulation, and possibly decreased coital frequency. From a large study of donor insemination, the strictly age-related reduction appears to be about one third for women aged 35 to 45 years. It is reasonable to begin the basic evaluation at 6 months in older patients and to consider starting treatment for unexplained infertility earlier in women older than 35 years of age.

Evaluation and therapy may be started earlier when obvious defects are identified, or they may be delayed, for instance, when a correctable factor, such as infrequent intercourse, is identified.

In general, the first 6 to 8 months of evaluation involve relatively simple and noninvasive tests and the performance of a radiologic evaluation of tubal patency (hysterosalpingography, or HSG), which can sometimes have a therapeutic effect. In some studies, use of an oil-based dye about doubled the success rate after HSG. Operative evaluation by laparoscopy is thus reserved for the small proportion of couples who have not conceived after 18 to 24 months or who have specific abnormalities or indications of a probable pelvic factor.

To keep the status of the evaluation in mind, it is helpful to arrange the workup under a series of five categories that can be mentally reviewed at each visit. Table 34-1 shows the approximate incidence and the tests involved in the evaluation of each category. Box 34-1 summarizes the treatment options for infertility. In 5% to 10% of couples, no explanation can be found (idiopathic infertility).

TABLE 34-1 COMMON INFERTILITY FACTORS

∗ Investigations only when menses are regular (every 22 to 35 days); oligomenorrhea generally requires treatment.