Effect of two non-steroidal antifertility agents on pregnancy in mice

Summary. The oral administration of clomiphene or U-11555A to mice appears to block pregnancy primarily through an effect on the maternal environment, rather than by direct action on the cleaving embryos. If given during the period of tubal transport, both agents cause a delay in the passage of the embryos into the uterus. When the compounds are given after the embryos have reached the uterus, implantation fails to occur, and the blastocysts pass out of the uterus. No evidence was found to suggest that pregnancy-blocking levels of the agents have a direct effect on the embryos