Sunday, October 30, 2005

How Does Emergency Contraception Work?

How does emergency contraception work? Glad you asked. Let's take a look at the available evidence.

First, some [oversimplified] basics.

What is emergency contraception (EC)?

EC is a group of birth control methods; the postcoital one, to be more exact. When you use a method from another group--an implant, the condom, Persona, sterilization--you use the method before, or during intercourse. When you use an EC method, you use it after you've already had sex. Again, what distinguishes the EC group from the other birth control groups is the timing of use. EC is postcoital (after sex) birth control; all the other methods are used before, or during intercourse:

An emergency contraceptive method is any drug or device used after an unprotected intercourse to prevent an unwanted pregnancy. It is, thus, a method that is used after coitus [sex] but before pregnancy occurs and is, therefore, not an abortifacient.


What are some of the methods in the EC group?

There are two types of EC methods: pills, and intrauterine devices (IUDs). The EC pills (ECPs) can be further subdivided into: high-dose estrogen; estrogen/progesterone (the combination Pill; Yuzpe regimen); progestin-only (Plan B); mifepristone (Mifeprex; RU486); etc. [Our discussion focuses on the pill methods.]:

Trials on emergency contraception were first described in the 1930s using high doses of stilbestrol. In the late 1970s, Yuzpe introduced a regimen consisting of 0.1 mg ethinylestradiol [estrogen] and 0.5 mg levonorgestrel [progestin], given within 72 h of the intercourse and repeated after 12 h.


The "Yuzpe" regimen basically entails using your regular brand of combination birth control pills on a modified, emergency contraception, regimen.

LNG [levonorgestrel] alone [Plan B] has been widely used in contraceptive formulations and has been used successfully for postcoital contraception as well. Higher efficacy and fewer side effects have been recorded when compared to the earlier method using an estrogen-gestagen combination [the "Yuzpe" regimen, or combination Pill]. A large multicenter study comparing the two regimens have shown LNG to prevent about 85% of the expected pregnancies if no other method was used.

Recently, treatment with levonorgestrel-only [Plan B] and mifepristone [Mifeprex, RU486] has emerged as the most effective hormonal methods with very low side effects.


An aside about mifepristone [Mifeprex, RU486]: Its mechanism of action is dose-, and regimen-dependent. When used as a single low dose ECP (older dosage 600 mg; current one, 10 mg), it acts as birth control and prevents pregnancy.

Theoretically, how should EC work to prevent a pregnancy?

Unprotected intercourse may occur at any time during the menstrual cycle but it is only during a limited period, from about 5 days before to 1 day after ovulation* that it may result in a pregnancy. To be effective, postcoital treatment could theoretically target one or several of the following events: sperm transport and function, follicular development [egg maturation, inside the ovary], ovulation, fertilization, embryo development and transport, implantation or the corpus luteum [what's left of the follicle, after the egg has been expelled; essential for early pregnancy support].


*[Recall that sperm may survive in the female reproductive tract for up to five days, and the mature egg may be fertilized over a 24-hour period.]

Second, let's look at what the studies tell us about ECP's mechanism of action.

How does EC work, in real life?

Human and animal studies have shown effects at several stages of the reproductive cycle: ovulation, fertilization, gamete transport, function of the corpus luteum and implantation.


The evidence shows ECPs work by preventing ovulation. There is no direct evidence they prevent fertilization. There's also no direct evidence they prevent implantation in humans.

Looking at ECPs' effect on:

Ovulation (release of mature egg from the ovary)

- inhibit or delay [established, main mechanism of action]

Fertilization (union of egg and sperm)

- no direct evidence for prevention [effect cannot be ruled out]

Gamete Transport

- no evidence of impaired transport in humans

Effects on the Function of the Corpus Luteum

- all pills disrupt this phase, however it is not known whether such changes are incompatible with pregnancy. [Better evidence for mifepristone vs. the other types of ECPs.]

Implantation (burrowing of a fertilized egg into uterus)

- ...although the postovulatory administration of estrogen or levonorgestrel inhibits implantation in some animals, evidence of similar
effects in women has been difficult to obtain. Minor changes in the histologic and biochemical features of the endometrium occur when high-dose estrogen, the estrogen/progestin combination, or danazol is administered after ovulation, but the effects may not be sufficient to inhibit implantation. In a recent morphometric study, postovulatory administration of estrogen plus progestin had only minor effects on the endometrium, and danazol had no effect.


- Mifepristone administered immediately after ovulation delays endometrial maturation

Bottom line:

...the proven mechanisms of action [of the hormones found in ECPs] consist of inhibiting or delaying ovulation.


and

An emergency contraceptive method is used after coitus but before pregnancy occurs....Recently, treatment with either 10 mg mifepristone [RU486] or 1.5 mg of levonorgestrel [~Plan B] has emerged as the most effective hormonal method for emergency contraception with very low side-effects. However, the knowledge of the mechanism of action of mifepristone and levonorgestrel in humans, when used for contraceptive purposes and especially for emergency contraception, remains incomplete.

...

When summarized, available data from studies in humans indicate that the contraceptive effects of both levonorgestrel and mifepristone, when used in single low doses for emergency contraception, involve either blockade or delay of ovulation, due to either prevention or delay of the LH surge, rather than to inhibition of implantation.


The last word goes to the NEJM (scroll to the bottom):

Use of emergency contraception is limited largely by ignorance. Although it seems likely that the estrogen/–progestin regimen works mainly by interfering with ovulation, it is nevertheless regarded by many as an abortifacient because it is taken after, rather than before, intercourse. This confusion is compounded when mifepristone is advocated for emergency contraception since, when taken after pregnancy is established, it can be and is used for the induction of abortion. The prevention of pregnancy before implantation is contraception and not abortion. Intervention within 72 hours after intercourse cannot possibly amount to abortion, because implantation is not achieved until at least seven days after ovulation and the egg is capable of being fertilized for only about 24 hours.


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[Pardon the abundance of tags; I've just discovered how to use them.]

Update: More here (via ourword)

Another Update: And make sure not to miss this post on Plan B from Pharyngula.

40 Comments:

At 4:00 PM, Blogger Bill Hooker said...

Thanks for this. (I had to correct a post in which I made the "prevents implantation" mistake.)

 
At 3:54 AM, Anonymous Anonymous said...

Same here.. thank you for the research, and correcting a misunderstanding I've had for a while.

 
At 12:32 AM, Anonymous Anonymous said...

Point of clarification, if the egg is fertilized, and it would go on to be implanted and turn into a fetus, how is preventing implantation not abortion? It is life in progress, not an unfertilized or non-ovulated egg.

 
At 1:46 AM, Blogger ema said...

Point of clarification, if the egg is fertilized, and it would go on to be implanted and turn into a fetus, how is preventing implantation not abortion? It is life in progress, not an unfertilized or non-ovulated egg.

First, a couple of clarifications. The majority of fertilized eggs are spontaneously aborted, so if an egg is fertilized, most likely it will not go on to be implanted. Moreover, just because a fertilized egg implants, does not mean it will progress to the fetal stage.

Second, abortion is defined as the termination of a pregnancy. A pregnancy is established only after implantation. Preventing implantation isn't abortion because a pregnancy hasn't been established yet.

Third, I'm not sure what you mean by "life in progress"? Anatomically/physiologically, a germ cell is as much life in progress at its incipient stages at it is at later stages.

 
At 9:05 PM, Anonymous Anonymous said...

"Second, abortion is defined as the termination of a pregnancy."

This is just using terminology to avoid the ethical issue. If a fertilized egg is a morally protected human life, then intentionally causing it to fail to implant is murder, whether it is technically abortion or not.

In the same way, "The majority of fertilized eggs are spontaneously aborted" is avoiding the issue. There is a clear moral difference between causing life to end and that end occuring naturally. If one lived in a time when the majority of children died before age of 5, would it be morally acceptable to kill your child? Of course not.

And finally, "I'm not sure what you mean by 'life in progress'?" seems laughable. The abortion debate has long used the phrase "the beginning of life" to refer to morally protected souls, and aside from the occasional scoffer commenting on how a wart is living human cells, no one is confused by this.

 
At 11:23 PM, Anonymous Manda said...

Who are you? Like, a doctor or something? Only reason I ask is that your post on ECP's was really informative and I wanted to know where you got your information since it's difficult to find unbiased sources on this topic (the religious ones call it evil; Planned Parenthood of course advocates totally in favor). Anyway, your post made me feel really relieved. Thanks so much. :-)

 
At 3:20 PM, Blogger ema said...

anonymous,

This is just using terminology to avoid the ethical issue. If a fertilized egg is a morally protected human life, then intentionally causing it to fail to implant is murder, whether it is technically abortion or not.

Using correct terminology is essential, in the real world. There's a significant difference, in terms of risk of morbidity and mortality between preventing a pregnancy (no implantation yet), and terminating one (post implantation).

You need to define morally protected human life in the context of a fertilized egg.

In the same way, "The majority of fertilized eggs are spontaneously aborted" is avoiding the issue. There is a clear moral difference between causing life to end and that end occurring naturally.

No, it's actually correcting your statement that ...if the egg is fertilized, and it would go on to be implanted and turn into a fetus...

Because the majority of fertilized eggs are spontaneously aborted, if the egg is fertilized, it would most likely not go on to implant.

And finally, "I'm not sure what you mean by 'life in progress'?" seems laughable. The abortion debate has long used the phrase "the beginning of life" to refer to morally protected souls, and aside from the occasional scoffer commenting on how a wart is living human cells, no one is confused by this.

I aim to amuse! In any case, reality is not defined by the terminology used by assorted ideological debates. I mean, please, "soul"; what does that mean? And, just for the record, a wart is, indeed, living human cells.

Manda,

Thank you. (I'm an Ob/Gyn.)

 
At 7:07 PM, Anonymous Anonymous said...

I'm doing research on all of this at the moment. All of your comments have been useful. The one thing I can't figure out is this: why there is an issue with ECP preventing implantation, since Birth control (daily estrogen/progestin oral contraceptives) also prevents implantation? I was previously totally against ECP, but after looking into it, I'm not so sure. i'd love to hear responses from both sides if anyone is still out there. - pharmacist

 
At 5:04 AM, Anonymous Anonymous said...

Regardless of whether or not you are using the correct medical terminology, it is misleading for the non-medical lay person to say that emergency contraception does not cause aboortion when it may work at preventing the implantation of an already fertilized egg. Many people would have a problem with this and they have the right to know in order to make an informed decision.

 
At 10:55 AM, Anonymous Anonymous said...

i had my first period a day after i took ECP but I have not had my second period yet. Is it normal for the second period to be delayed by a week or so. My first period was normal.

 
At 11:07 AM, Anonymous Anonymous said...

Hello everyone! I m really not sure whether birth control pills delay period cycle or not?Let me explain what do I mean...For last 15 days I was taking Birth control pill to prevent pregnancy...that is I did sex with my husband on 31st Jan without Condom and I started to take pills from 2nd Feb,which I skipped on 3rd Feb and restarted from 4th Feb.From yesterday(18th Feb,)I have stopped taking pills as my period date was 17th Feb,which is over and period haven't stared yet,However,I don't think, I m pregnant as my husband didn't discharge sperm inside my Vagina and I don't have any symptoms of pregnancy...I just started taking pills to prevent any chance of becoming pregnent...now this is 20th Feb,but no period..why?Can anyone help me?

 
At 11:10 AM, Anonymous Anonymous said...

Pls help

 
At 6:26 PM, Anonymous Anonymous said...

Hi! not sure if I'm pregnat had last menstural cycle on 03/02/07 ended on 07/02/07. Had intercourse on 17/02/07,18/02/07 and 21/07/07 respectively. Then on 03/03/07. However I used the morning after pill Postinor-2 immediately after my last encounter. My period is now a little late not sure if its because of the use of the pill. Can you provide answers to this

 
At 9:18 AM, Anonymous Anonymous said...

hi. i have a question, i had unprotected sex on friday morning then later took the emergency after pills and following that i had sex with a condom, but it broke. he might of precumed, im not sure. but will the emergency after pills work for that night too? i got scared and took a pill of the birth control. but i really dont want to take birth control pills. please answer me back a.s.a.p

 
At 4:53 AM, Blogger highlyeccentric said...

If EC works primarily by preventing ovulation, not by preveting implantation, what happens if you ovulated in the 24 hours BEFORE having sex? Your ovum can still be fertilised, am i correct? and so you just hope it doesn't implant?

 
At 1:30 AM, Blogger Sonia said...

thanks so much for this.! it's great to know some people are educated on the subject.

to those who think the *possibility* that a fertilized egg *MIGHT* be prevented from implantation=abortion, well, i hope they realize that our bodies naturally reject fertilized eggs from implanting all the time.
essentially the EC pills are ensuring our bodies will do something they do naturally on occasion anyway.

 
At 2:37 AM, Anonymous Anonymous said...

"The prevention of pregnancy before implantation is contraception and not abortion."

That is only if you accept the definition of the American College of Obstetricians and Gynecologists (ACOG). They changed their definition of pregnancy back in the 60's so that they could call EC contraception and not an abortifacient. If you look at most other medical fields and practically any medical or common dictionary they still define pregnancy as beginning with fertilization NOT implantation. If that is the case, then EC's would be abortifacient...as would most methods of hormonal birth control.

Here are just a few sample definitions from medical dictionaries:
Mosby’s Medical dictionary, 7th Edition, (c) 2006

Conception (l, concipere, to take together), 1. The beginning of pregnancy, usually taken to be the instant that a spermatozoon enters an ovum and forms a viable zygote. 2. the act or process of fertilization

Pregnancy: The gestational process, comprising the growth and development within a woman of a new individual from conception through the embryonic and fetal periods to birth.

Stedman’s Medical Dictionary, 28th Edition, (c) 2006

Conception. 3. Fertilziation of oocyte by a sperm (latin conception; see concept)

Pregnancy: The state of the female after conception and until the termination of the gestation.

 
At 12:23 AM, Anonymous Anonymous said...

does ec works after 15 days ov intercross

 
At 3:33 PM, Blogger ema said...

Anon @ 12:23 AM,

No, it does not. ECPs work best if you take them as soon as possible after the act of unprotected intercourse, up to 120 hrs (5 days).

Anon @ 2:37 AM,

Your tactic of using dictionary definitions is noted but, even so, you do realize that I am bound by a blood oath to accept ACOG's, well pretty much anything, no?

On a more serious note, conceptus and pregnancy are not one and the same. One term refers to a bunch of tissues (embryo, membranes, and placenta), the other to a physiological state.

Also, as much as conspiracy theory moves like the one you mentioned are, you know, part of standard medical science, you'll no doubt be disappointed to find out that no such move was needed for ECPs. [See ECPs mechanism of action.]

Last, but no least, fertilization is not an instantaneous process, and its result is a bunch of totipotent cells.

 
At 3:33 PM, Anonymous Anonymous said...

im having problem…i had sex last october 19,2010..my first day of menstruation was on october 6,2010..5 days of menstruation..i had no contraceptive used…two days from now, im worried if i will get pregnant…pls help me…what pill could i effectively take w/out side effects to prevent pergnancy????thank u…

 
At 8:59 AM, Anonymous Anonymous said...

i was told to take the ecp 1*2 after unprotected sex. however i forgot to take the next pill in 12hrs but only remembered to take 15 hrs apart. i am safe? should i repeat the doze?

 
At 9:01 AM, Anonymous Anonymous said...

for how long does ecp work in the body after taking it.

 
At 8:00 AM, Anonymous Anonymous said...

Does postinor 2 work during ovulation?

 
At 3:10 AM, Anonymous Anonymous said...

does postinor 2 work during ovulation?

thats when it really has to work right? ust hopefully it does. Nothing is ever 100% fool proof, but ECPs also have a high success rate. Should work in my opinion.

 
At 11:53 AM, Anonymous Anonymous said...

My comment is directed at the people who posted regarding having sex and not knowing if they may or may not be pregnant. If you aren't informed about your chosen method of birth control or about sexual intercourse, you shouldn't be having UNPROTECTED sex. Even while taking oral contraceptives on time without missing a dose still leaves an 8% chance on average of getting pregnant. Skipping 1 pill won't lower effectiveness but you must take 2 pills on the next dose...missing more than one pill requires the use of a condom or something else to prevent pregnancy. The only way to avoid getting pregnant 100% is to abstain, and I am not saying that you should abstain, just UNDERSTAND the risks that you are taking when you have unprotected sex especially with regard to pregnancy. It's a liftime responsibility.

 
At 6:48 AM, Anonymous Anonymous said...

HEYYY EVERYONE I NEED HELP i usually get my period evry 3 weeks because its irregular...but last month it came in 2 weeks(one week earlier)...i had unprotected sex in the 2nd week while i was expecting it to come..the followin day i took the pill and now its more than 8 days late(since i thought it would come in the 2nd week, but ill wait another week which is my USUAL time for it to come,3 weeks)..ive been experiencing slight cramps and more urination..MAY I BE PREGNANT and WHAT ARE THE CHANCES OF THE PILL SUCCEEDINg?

 
At 11:22 PM, Anonymous Anonymous said...

i had sex on day twelve of my cycle then i took postinor on day thirteen , however i again had unprotected sex eight days later but my period has not come one week later am ipregnant? Help!

 
At 3:18 PM, Anonymous Anonymous said...

Hi thank you for the information. I'm not pregnant or afraid I may be I was just curious as to how EC works. I just want to make sure I understand correctly. EC only works to delay ovulation. So there for if you have already ovulated and you have sex with in that short window that the egg is likely to get fertilized than there is no confirmed evidence that EC will stop anything from happening. To my understanding it is only if you take it with in the 5 days that the sperm is alive and you are due to ovulate that you may be able to delay ovulation until the sperm has died and then ovulate hopefully after. Is that correct? Further more about the debate on If it is religiously or morally correct, If I wanted to know what a religion felt about the issue I would have looked that up. I feel that science should stay in science and religion should stay in religion. Women should research which both or either depending on their views before making decisions like this. I would say the same if someone was pushing science in a moral argument. It has it's place but that is not what this about. The arguement between the exact moment to call it an abortion is a valid one I see both sides but I feel that when it comes to EC it is every woman's responsibility to choose how they feel about it. It is their choice to live with either way. They need to be presented with unbiased information and then take that information and choose how they feel about it morally or religiously. To the women who are worried about if they are pregnant or not, it is nearly impossible to tell if you are pregnant by telling us when you had sex. It all depends on when your body ovulated. If you are late take a pregnancy test. If it says no and you continue to be late call your doctor it may be a health problem. Please do your research about these issues proir to making choices that can lead to pregnancy. These things should not be something you scramble to learn about after you have unprotected sex. A baby is too important to be making quick uneducated decisions about. Lastly is there any evidence that if EC is taken after conception has occurred that the high doses of hormones can effect the development of the fetus? That would be my concern. I think that most women who have taken EC feel they are not ready to be moms. They surely then are not ready to be mothers of disabled children. Is there any evidence at all that babies who were exposed to EC have any higher rates of issues of any kind? - pharmacy tech, mother, and believer of science and informed choices.

 
At 2:59 PM, Anonymous mom25 said...

This things helps me a lot on what i experience.im a mother of 3.i use contraceptive pills after my 3rd kid.but because i experience lots of side effect and the onethat bother me most is not having my period while using it so i stop and use the natural way.one time i had sex with my husbnd he accidentaly precumed inside which made me worry a lot because i m sure im not safe because its my ovulation period so the next day i try using EC which i found on the net.i cnt fully understand how it works i just knew it can be use to prevnt pregnancy after unprotected intercourse.i had few days of intercourse after thAT.2 weeks ater using EC i had spotting that is bwownish that last two days,i thought its gonna be the sign that my period will come that is due that week.i experienced crmping and sore breast so i worried it maybe sign of early pregnancy even my due date s not yet come.to make sure i can still avoid to get pregnant i search for abortion proceSS and found that vitamin c was one of the safe home abortion i tried it without testing if im really pregnant eventhough i got the first PT negatve that i took after the brown discharge.after 6 days of using vitc and parsley tea no period at all,i stoped and after a day i test again bt still negative bt no sign of period so i decided to see my obgyne to make sure if im pregnant or not,maybe all that i suffered is side effect of ECP,who knows?ill have to wait for the result of a true expert..i just wnt to add,its very important for us woman to know everything about this matter"cycle for the beginning of life that starts with us women.we're the number responsible for it.we can alsthe only who will truly educate our partners for cooperation what they should really know so everything will end responsibly for a new given life.

 
At 4:35 PM, Anonymous Anonymous said...

After having sex again immediately after taking the second pill will the second pill help in preventing pregnancy?

 
At 5:22 AM, Blogger ema said...

Anon @ 4:35 PM,

It's the full dose (2 pills) that works to prevent the pregnancy, not each pill, individually. That having been said, you're probably still protected. For the future, consider that one dose (2 pills) only covers *one* act of unprotected intercourse and use a regular method of birth control, like the Pill, NuvaRing, IUD, condom, etc.

 
At 2:40 PM, Anonymous Anonymous said...

does emergency contraceptives work on 3 weeks pregnant,reply pls

 
At 8:26 PM, Anonymous Anonymous said...

If I had sex with a condom before ovulation, took the MAP 7-8 hours after intercourse, the odds of being pregnant are slim, correct?

 
At 7:56 AM, Anonymous Anonymous said...

So wait, if sperm can live in the body for 5 days, is it possible to take EC and ovulate a day or two after while the sperm is still alive?

 
At 6:18 PM, Anonymous Anonymous said...

Hey i have a question please do answer cuz m really worried i have to go to abroad for studies and cant risk pregnancy , umm me and my bf messed up each other. The other day i took the contraceptive and a week later i had bleeding for 4 days (used two pads a day) along with light cramping so was that my period ?? Because ecp must have been altered my cycle the last date of my periods was 24,4,14 and took the pill on 3 bled on 9 or 10 please help

 
At 5:23 PM, Anonymous Anonymous said...

My period was July 1st 2014 to July6 2014 I had unprotected sex early morning of July 11 2014 I took the EC pill today am I safe from becoming pregnant?

 
At 5:33 PM, Anonymous Anonymous said...

I had a period July 1st 2014 to July 6th 2014 I had unprotected sex late Thursday night Early Friday morning (July 11th) I just took the EC pill Today about 11am am I protected or is it possible I could be pregnant?

 
At 4:36 AM, Anonymous grace said...

I had sex during d period I was ovulating..took postinor 2 exactly 2hrs after..pls am scared..dont know if d drug will work since I was ovulating..pls help

 
At 8:24 AM, Anonymous Anonymous said...

had sex during ovulation, took postinor 2hrs after..pls will i get prgnant cos im scared... will the postinor work

 
At 4:35 AM, Anonymous Anonymous said...

I took postinor after 5 days. Will it work? Pls help

 

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