Conception rate according to semen characteristics in a series of 15 364 insemination cycles: results of a multivariate analysis.

The study was undertaken on 1438 ejaculates from 342 donors. The sperm count, volume, prefreeze and postthaw motility were evaluated for each ejaculate and the morphology for the first ejaculate of each donor. The success rate was found to increase steadily with the sperm count, prefreeze and postthaw motility. For the volume and percentage of all abnormal forms, the success rates are stable up to 5,5 ml and 40% respectively and then decrease. Among all the abnormal forms considered, only the microcephalics and irregular heads were found to be linked to the success rate. As most of the studied characteristics are correlated, a multiple stepwise regression was completed in order to determine the proper role of each variable. The most predictive variable is the postthaw motility. The second variable is the percentage of microcephalics. The other variables bring no further information. In particular, at a given postthaw motility, the prefreeze motility and consequently, the loss in motility have no influence on the success rate.