Low dose of ethinyl estradiol can reverse the antiestrogenic effects of clomiphene citrate on endometrium.

Fifty healthy, voluntary patients aged between 20 and 30 years with regular menstruation and plasmatic progesterone level >10 ng/ml at the midluteal phase have been enrolled in this study. They were randomly treated with clomiphene citrate (CC; group A) or CC + ethinyl estradiol (0.05 mg group B, or 0.02 mg group C). We estimated the difference in uterine artery pulsatily index, endometrial thickness and histological dating and morphometric analysis of endometrium. No significant differences in Pulsatility Index values and in the number of preovulatory follicles were noted. The difference between endometrial thickness, histological dating and morphometric analysis of the endometrium were statistically different between groups B and C vs. A. Our study shows that CC has a deleterious effect on endometrium maturity and that adding ethinyl-E(2) produces a favorable endometrial response even with very low doses.