Transabdominal ultrasonographic evaluation of endometrial thickness in clomiphene citrate‐stimulated cycles in relation to conception

The possible antiestrogenic effect of clomiphene citrate on endometrial growth was assessed by serial transabdominal ultrasonographic measurements in 46 women with unexplained infertility. A significantly higher ( p < 0.05) rate of endometrial growth was observed in the 8 women who conceived compared with the 38 women who failed to conceive. A thicker endometrium (4.6 ± 0.3 mm) was observed from the third day before ovulation as well as a higher average growth rate in the three days prior to ovulation (0.7 ± 0.1 mm/day) in the group that achieved pregnancy compared to a lower endometrium (2.1 ± 0.2 mm) from the third day before ovulation and a slower growth rate in the three days prior to ovulation (0.2 ± 0.0 mm/day) in the group that did not achieve pregnancy ( p < 0.05). These data suggest that clomiphene citrate may exert an antiestrogenic effect on the endometrium, and thus interfere with implantation. © 1994 John Wiley & Sons, Inc.