The importance of egg and sperm factors in predicting the likelihood of pregnancy from gamete intrafallopian transfer.

The relative contribution of factors affecting the probability of pregnancy from gamete intrafallopian transfer was estimated using data from 218 cycles performed in San Antonio, Texas, and Orange, California. Mature eggs, all of which contained an expanded cumulus, were subclassified according to the corona radiata; those with a starburst corona were considered the most fully mature. Sixty-two clinical pregnancies were established, representing a pregnancy rate of 28.4%. Excluding 49 cases of male factor infertility, the pregnancy rate was 34.9%. Pregnancy rates were not significantly different according to age, cause of female factor infertility, parity, duration of infertility, stimulation protocol, or estradiol level. The only variables having a strong association with pregnancy were sperm and egg parameters. Sperm motility and morphology were statistically more important than sperm density. Based on odds ratios calculated from multiple logistic analysis, pregnancy was 3.80 times more likely if three or more fully mature eggs were transferred, 0.34 times as likely if motility were less than or equal to 30%, and 0.22 times as likely if normal morphology was less than or equal to 50%, controlling for other egg and sperm factors. If all egg and sperm factors in a given cycle were unfavorable, the probability of pregnancy estimated by the logistic model was 4%, whereas if all were favorable the probability of pregnancy in that cycle was 59%.