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.
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.
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.
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%. 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.
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.
Right now there are three FDA-approved preparations available: Next Choice, Plan B One Step, and ella. Next Choice and Plan B One Step are sold over-the-counter to women age 17 and older. They are available for younger women by prescription. Ella is available by prescription only. The cost of these medications is around $40.
Side effects with progesterone derived EC’s are minimal—headache, menstrual pain, nausea, dizziness, and abdominal pain may occur. Because of the extremely brief exposure to the medication, these effects are short-lived.
Although these drugs are contraindicated in a person known to be pregnant, should they be taken during a pregnancy or should a woman who takes EC become pregnant and decide to continue with her pregnancy, there is no evidence of fetal harm from having used EC.
You took EC. You have reduced your risk of getting pregnant. Now what? You wait, essentially for your next period to come. Under no circumstances should you have unprotected intercourse. Should you decide to have sex before your period, use protection, preferably double protection, the male condom plus the diaphragm, sponge, gel, or foam.
After taking EC and as you are waiting for your period, you may experience certain symptoms. Some women get bleeding or spotting shortly after taking EC. Most women will get their period within three days of the expected date. Women who took levonorgestrel may be a little early; those who took ulipristal may be slightly late. If you have not gotten your period in 21 days, get a pregnancy test and seek medical attention.
Positive pregnancy test or not, this is a great time to see your physician or attend a family planning clinic and have a serious talk about contraception. There are many different choices, depending on your personal situation. Emergency contraception is just that — a good option in an emergency, but it's not a replacement for planned birth control protection.