Simple model and empirical method for the estimation of spontaneous pregnancies in couples consulting for infertility

Based on simple theoretical models and on the analysis of data of over 12,000 couples, a simple formula is proposed to predict the probability of spontaneous (treatment-independent) pregnancies in couples consulting for infertility after at least 12 months of unprotected intercourse. For a duration of infertility of between 12 months and 48 months the probability of conception per cycle of exposure is 4 X 0.97n X (a) X (bm) X (bf), where n is the number of months of unsuccessful trial to conceive, a refers to the type of infertility (primary vs secondary), bm depends on the severity of impairment of semen parameters, and bf relates to the age and pathology of the female partner. Some tentative values for these factors are calculated.