Why does emergency contraception have to be taken within 72 hours?

what i suppose i mean is, what happens to your body to make the pill unaffective after this time, also what would be the earliest sign of pregnancy after conception?

Because the morning after Pill is taken to prevent a pregnancy from establishing (before the fertilised egg implants in the uterus). After 72 hours the pregnancy will have established, thus the action of the drug will no longer be effective.

The effect is determined by the time in the cycle it is taken.

The pill contains high levels of progesterone & oestrogen. It causes the cervical mucus to become thick & sticky (preventing movement of sperm).

The pill can also mimic early pregnancy, this prevents an egg being released by inhibiting the release of the hormone FSH (egg stimulator) which releases eggs.

The MAIN use of the emergency pill (in emergencies) :
Oestrogen & progesterone prevent implantation, so a fertilised egg cannot implant into the wall of the endometrium (the side of the uterus) & instead it is ejected with the endometrium at the end of the cycle.
^ this is usually why it is used, it prevents a fertilised egg from growing into a foetus by ejecting it.

IF it's taken too late:
The above won't happen. A fertlised egg would implant (a fertilised egg takes just 48 hours to reach the endometrium & implant). Thick & sticky cervical mucus wouldn't take effect because the sperm will be past it. & an egg would probably have already been released (depending on what stage in the cycle) so inhibition of FSH would be useless.

I hope this helps

"Studies show that both types of emergency contraceptive pills can prevent or delay ovulation (the time in your cycle when your ovaries release an egg). If you take emergency contraceptive pills before fertilization (the point when the egg and sperm meet), they may interfere with the process of fertilizing the egg, for instance making it harder for the egg or the sperm to travel (and meet up) in your reproductive tract. It鈥檚 also possible that emergency contraceptive pills work after fertilization, making it impossible for the fertilized egg to implant in your uterus; however, the best available evidence suggests that ECPs鈥?ability to prevent pregnancy can be fully accounted for by mechanisms that do not involve interference with post-fertilization events."

http://ec.princeton.edu/questions/ecwork...

You don't have a lot of time before fertilization occurs, so you want to get the pills taken as soon as possible BEFORE that happens.

Because the damage is usually done in three days. Three days is the average life span of a sperm cell. They either fertilized an egg during that time, or they didn't. There was either an egg there to fertilize, or there wasn't. If you ovulated during that time, no pill in the world is going to make you un-ovulate.

It might interfere with implantation, or it might not. Plenty of women get pregnant even after emergency contraception.

There aren't any symptoms until after implantation, which could take anywhere from six to twelve days to happen. Your first symptom is likely to be a late period and a positive pregnancy test.

what emergency contraception does is, it stops the sperm from getting to the egg, or if it has already been fertilised, it stops the egg from latching onto the wall of your insides if you get me

after this has been done, however, you are well and truely preggers and the emergency pill can do nothing for you

I believe that it is going to try to kill the sperm off before it reaches your eggs. Sperm can live for I believe 7 days in you before all of them are dead. So waiting so long before taking it would be insufficient. Check out this website and I hope it helps. http://www.fwhc.org/birth-control/ecinfo...

after 72 hours the egg will have implanted in the endometrial tissue in the uterus and the pill not only will not prevent pregnancy it will cause birth defects in the fetus.

the medicine in the pill thickens the walls of a uterus so the sperm cannot meet with the egg. it also prevents the ovaries from releasing an egg. the combination of the two makes it almost impossible to conceive

safer if you take before ovum gets fertilized by sperm and gets implanted in uterine mucosa.early signs starts after 1 month as vomit ting tiredness appetite loss etc. better have pregnancy test. earliest result you can get nowadays

it because the pill works by stopping the egg getting implanted into the womb.

after 72 hours its going to be implanted therefore ill not work

It needs to be taken before the fertilized egg implants in the uterus.

I'm guessing it's probably before the egg implants into the uterine wall.

Because the directions say so

it would be to late cos the egg or wateva would of already been fertilised

When your pregnant you'll know why.