The mean of sperm parameters in semen donations from the same donor. An important prognostic factor in insemination

We analysed 12,100 consecutive cycles of artificial insemination by donor spermatozoa in 1901 infertile couples. In our analysis, particular attention was given to finding an appropriate way of taking into account the respective effects of female and male factors on the pregnancy success rate and the level at which these factors act (cycle vs. woman and donation vs. donor). A total of 1213 pregnancies occurred. The pregnancy rate per cycle was lower as the age of the woman increased (p < 0.0001) and varied with the type of infertility: fecundity was higher (p = 0.03) in the case of azoospermia than of severe oligozoospermia. After taking into account these factors, significant unexplained variation in likelihood to conceive remained. A part of this heterogeneity was shown to be due to variation in fecundability between semen donors. In order to explain this heterogeneity between donors, compositional covariates were used, particularly the mean of results of the semen analysis performed for donations from the same donor. For each semen characteristic, the overall mean of the different donations of a donor was an important predictive factor of successful insemination: after taking into account all of the other factors, the odds ratios for an increase of 50 x 10(6)/mL spermatozoa, of a 20% increase in sperm motility and of a 2 point increase in the post-thaw quality index, were, respectively, 1.13, 1.37 and 1.56. After adjustment for these factors, the specific characteristics of each semen donation were no longer significantly predictive of successful insemination. This observation has a biological interpretation: sperm with low parameters but produced by a normally fertile man can have a satisfactory success rate.