Top of page Does Plan B Interfere with Implantation of the ova into the uterus?
If Plan B interferes with implantation, it should be capable of preventing pregnancy when it is used after the process of fertilization. In a recent clinical studies in which timing of ovulation was determined quite precisely using hormonal criteria (FSH, LH, progesterone and estrogen), no pregnancies occurred in the 34 women who had unprotected intercourse 2 to 5 days before ovulation occurred and took 1.5mg of levonorgestrel before or right at the time of ovulation, no pregnancies occurred. 4 or 5 pregnancies would have been expected in this group. For those women who had intercourse 24 hours before or the day of ovulation and took Plan B 48 hours or longer after ovulation had taken place, 3 pregnancies occurred in 17 women which 3 or 4 were expected to get pregnant without the use of Emergency Contraceptive pills. These studies strongly suggest that Emergency Contraception does not interfere with implantation. If Plan B interferes with implantation, its efficacy should not decrease
