A prospective study of prognostic factors in in vitro fertilization and embryo transfer.

Multiple factors influence the outcome of in vitro fertilization and embryo transfer (IVF-ET). This prospective study was designed to assess their relative importance, in order to improve prognostic ability and treatment success. Prior to IVF-ET, couples were divided into "good" (GP) and "poor" (PP) prognosis groups according to female age, semen quality, previous response to stimulation, and embryo quality. The data obtained from 716 consecutive treatment cycles then were evaluated using univariate statistics and logistic regression, a technique designed to assess the relative contribution of significant factors. The pregnancy rate per GP cycle was 14.7%, compared with 5.4% per PP cycle (chi 1(2) = 12.7, P less than 0.001). The most important prognostic factors were female age, the pregnancy rate showing a linear decline after the age of 25, and previous failed fertilization due to abnormal sperm. The rate of pregnancy also declined after 14 or more follicles were aspirated and/or nine oocytes were retrieved. A formula for the probability of pregnancy, derived from the logistic regression, provides patients with a more accurate prognosis before treatment.