Does Plan B Interfere With Sperm Migration?
Plan B (emergency contraceptive pill, morning after pill, day after pill, post coital contraception, day after contraception) does not directly interfere with the sperms ability to fertilize an ova. Plan B is able to alkalinize the intrauterine cavity fluid after 5 hours of ingestion which is turn reduces the number of sperm recovered and immobilizes sperm so that they can no longer swim towards the fallopian tube. In approximately 9 hours after ingestion of levonorgestrel, significant thickening to the cervical mucus takes place which prevents further sperm from able to penetrate the cervix. It is obvious that alkalinization of the uterus and thickening of the cervical mucus develop too late to prevent the onset of the initial migration of sperm and therefore cannot be the primary mechanism of how Plan B reduces the pregnancy rate. Ejaculated mammalian spermatozoa reside in the female genital tract for several hours before gaining the ability to fertilize the egg. The sperm cells unde
