Mechanisms of action of oral emergency contraception.
We investigated whether the expression of progesterone-binding sites on human sperm acrozomal membrane is correlated with in vitro fertilization outcome. In motile sperm we evaluated percentage of progesterone-binding sperm (%PB) and of acrozome-reacted sperm (%AR), collected from 39 male partners undergoing an in vitro fertilization program (IVF), by labeling the sperm with progesterone-conjugated BSA-labeled FITC (P-BSA-FITC) and pisum sativum agglutinin labeled-FITC (PSA-FITC). Mean %PB in 30 fertilized cases was significantly higher than that in 9 fertilization failures (9.0 +/- 5.1 vs. 22.3 +/- 14.8%, p < 0.01). Furthermore, %PB shows a strong positive correlation with fertilization rate in IVF (r = 0.44) and %AR (r = 0.62), but not with sperm concentration and sperm motility. These results suggest that the expression of progesterone receptor on the sperm was related to the sperm fertilizability, and the evaluation of %PB was useful for predicting the fertilization outcome of IVF.