Does Plan B Interrupt Fallopian Tube Function?
Fertilization takes place in the fallopian tube. There are studies in animals that show that estrogen and progesterone can speed up or slow down the transport of ova in the fallopian tube. Therefore; Plan B could indirectly prevent pregnancy by interrupting the transport of fertilized ova through the fallopian tube and by the time the ova arrives in the uterus, it is not able to implant or undergo the decidualization process. If Plan B (morning after pill, day after pill, post coital contraception or day after contraception) does slow down movement of the ova through the oviduct there should be an increased risk of ectopic pregnancy. Combined data from several clinical trials involving nearly 6000 women showed the actual rate of ectopic pregnancies in women who had used Plan B to be 1.02%, which is slightly lower than overall national ectopic pregnancy rates (1.24%-1.97%). This does not show that Plan B prevents normal movement of the fertilized ova through the fallopian tube.
