March 03, 2015
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Emergency Contraception: What You Need to Know
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Emergency Contraception: What You Need to Know


You are a woman of childbearing age.
You had sexual intercourse without contraception.
You do not wish to be pregnant.
What is your risk of getting pregnant?

This is a scenario familiar to many women. Pregnancy can only occur around the time of ovulation, the time when the ovary releases an egg into the fallopian tube. Ovulation occurs midway between menstrual periods if your periods are regular. In medical practice we call the first day of the menstrual period, "day one." The time of ovulation usually occurs midway between first day of two successive periods, but it can vary from day 8 to day 20 of a 28 day cycle.

Figuring the Odds of Being Pregnant

The middle two weeks of your cycle is the time you are most likely to get pregnant. Most women ovulate around day 14, but there is great variation. The time of highest risk for unprotected sex is one or two days before ovulation when there is a 30% chance of becoming pregnant. Three days before ovulation the risk is 15%; on the day of ovulation it is 12%; after ovulation the risk approaches zero.(1)

Women with irregular cycles have more trouble determining when ovulation is occurring. There is a symptom called "mittelschmerz," a term meaning "pain in the middle," that occurs on one side of the abdomen at the time of ovulation. It is caused by spillage of the fluid in the bubble that surrounded the egg when it was on the surface of the ovary and about to be released. That fluid can irritate sensitive surfaces of the abdominal lining and the bowel.

The pain of mittelschmerz is usually deep in the pelvis and can go on for about 12 hours. The monthly pain of mittelschmerz will alternate from one side of the pelvis to the other, because the right and left ovaries take turns ovulating. Not all women experience mittelschmerz, but those who do will have a good idea of when ovulation is occurring in a given cycle. This is true for women with regular or irregular cycles.

So let’s say that you are a woman who gets mittelschmerz, and the day after you had unprotected sex, you felt it. You are at very high risk for getting pregnant—up to 30%.

In the real world, in large studies of women who have unprotected sex in mid-cycle, the risk of getting pregnant is much lower—5-8%.(2) This is because sexual relations on any day other than the 3 days before and the day of ovulation have a very low risk of resulting in a pregnancy.

In the real world, there are other circumstances calling for emergency contraception. One would be an obvious failure of a barrier contraceptive, like a condom with a tear in it. Another is a case of sexual assault, when a woman is raped.

Lowering Your Risk of Pregnancy with Emergency Contraception

So let’s go back to our original line of questioning: What can you do to lower your risk of getting pregnant in these circumstances? You can use emergency contraception (EC). It can decrease the likelihood of getting pregnant by 50-70%. That means that instead of a 5-8% chance of getting pregnant, your chance would be 1-4%. The word "emergency" and the term "the morning after pill" are very apt. You have to get this medication and take it as soon as possible. The sooner you take it, the lower the risk of getting pregnant. The medications described here can be effective up to 5 days after unprotected sex, but their effects decrease with time.

Hormonal Emergency Contraception (EC)
These medications consist of female hormones or derivatives of female hormones that can work in several different ways. The most important effect is a delay in ovulation. Other possible effects are changing the function of the fallopian tubes or altering the lining of the uterus so that a fertilized egg will not implant.

The Copper Intrauterine Device (IUD)
Another effective method of EC is to have an copper IUD placed within 5 days of unprotected sex. This is effective primarily by altering the uterine lining. You need to see a gynecologist to have an IUD inserted.

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