Prognostic parameters in predicting pregnancy: A twenty‐year follow‐up study comprising semen analysis in 765 men of infertile couples evaluated by the Cox regression model

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Abstract
The Cox proportional hazard regression model was employed on 765 infertile men whose semen had been analysed in 1950 and 1951 and who replied to a questionnaire 20 years later. Of nine clinical and laboratory variables evaluated, four possessed significant and independent prognostic information about the time required to conceive, when covariation between the variables was considered. They were: age of the man at semen analysis, percentage normal spermatozoa, percentage mobile spermatozoa, and the degree of motility. The four variables were combined to form a prognostic index, which permits prediction of individual pregnancy probability. The five variables which possessed no significant prognostic information were time from ejaculation to semen analysis, period of abstinence, existence of previous pregnancy, volume and sperm count. There was a satisfactory agreement between predicted and observed pregnancies in the present series. Thus, the index may prove clinically useful. However, its value must be established in other independent series.