36 - Unexplained Infertility

Summary

INTRODUCTION

Human beings are not very fertile mammals, with an average monthly fecundity rate of only 20 percent. Formal evaluation of infertility is generally indicated in women attempting pregnancy who fail to conceive after a year or more of regular, unprotected intercourse; 85 percent of couples who will achieve pregnancy without assistance succeed within this interval of time (1,2). However, most couples seeking therapy for infertility are not truly sterile but have some degree of subfertility (i.e., the couples have conditions associated with a relative decrease in the monthly likelihood of conception) and can achieve pregnancy without treatment (1,3,4). Thus, in contrast to the treatment of sterility, it cannot be assumed that the pregnancy that occurs after treatment for subfertility is attributable solely to the treatment because it could have occurred by chance. Such treatment-independent pregnancies are more likely in couples designated as having unexplained infertility.

Despite advances in the diagnosis of causes of subfertility, inability to conceive remains unexplained in 15–30 percent of fully investigated couples (1,5). In these couples, the delay in conception may represent a chance delay or may be, in many cases, the result of an as yet undetected abnormality in the reproductive process. Cumulative pregnancy rates of 60 percent may be achieved within two years; however, for infertility of greater than three years duration, monthly fecundity rates in untreated couples are 1–2 percent (6,7).