Dr Rick

Hormonal emergency contraception is believed to work in one of three ways depending on where the woman is in her menstrual cycle at the time of treatment. It can delay or prevent ovulation, impair formation of the corpus luteum, or cause histological or biochemical changes within the endometrium.

It's not clear which one of these three prevails. The later two allow fertilization to occur but prevent pregnancy by blocking implantation of a fertilized ovum.

Rick

Daleth

Thanks, Dr. Rick. That is what I thought I knew.

Dal

RevDahlia

I stand corrected, thanks guys. Still think that fatherphil was confusing the morning-after pill with RU-486, though, judging from the wording he used originally. Important to make that distinction.

Dr Rick

...However, you are quite correct that hormonal emergency contraception (EC) is not an abortifacient. An abortion can only occur in a pregnant women, and a women is pregnant only when she has an implanted embryo/fetus. Pregnancy, which is a maternal and not fetal condition, does not begin at the time of conception because there is absolutely no physiologic or biochemical change brought about to the mother by fertilization of an ovum. It is only upon implantation that the woman is pregnant and any change in the physiology of the woman can be observed. The IUD, EC, and birth control pills are not abortifacients, but RU-486 is.

Daleth

And again, thanks, Dr Rick. I was about to post the same, but wouldn't have said it as well.

Dal

Dr Rick

Yor're most welcome

scigirl

I started a thread in science and skepticism about this very topic - you can find it here.

scigirl

openeyes

I was just at a seminar about emergency contraception last week. A woman from the company that developed "Plan B", the progestin only EC formulation, said that in their studies, it appears that in almost all cases, the "pills" (it's actually 2 tablets taken 12 hours apart) work by preventing ovulation. They can't rule out impeding fertilization or implantation, but they can't say that regular birth control pills don't occasionally work that way also.

Once ovulation has occured, the ovum is only viable for about 24 hours. Sperm can hang around for up to 5 days and still be viable, so it's pre-ovulation that's the main danger time. (I know some of these points are addressed in your thread scigirl, but since there's so much misinformation about EC, I thought I'd say it again.) The sooner a woman takes the regiment after unprotected intercourse the better, but there is effectiveness up to 5 days. Once implantation occurs, they don't work (but they don't do any harm).

A pharmacist from Washington State said that once EC became more readily available through a pharmacist without going to a clinic, the abortion rate dropped 30% in that state. Medicaid also saved $22 million because of fewer children born to lower income women.

Plan B could be over-the-counter within a year if the FDA approves.