While there are several options for emergency contraception, they generally fall into two categories: hormonal and non-hormonal-based approaches. Choosing which option is best for you requires consideration of several factors, including the availability of the contraceptive, drug side effect profiles, risks, costs and long-term contraceptive needs. It also depends on the time elapsed between unprotected sex and availability of the emergency contraceptive.
We now review the different types of emergency contraceptive options and discuss their mechanism of action (how they work to keep you from getting pregnant), delivery route, and their advantages and disadvantages.
Hormonal Emergency Contraception
In the normal menstrual cycle, hormones from the brain stimulate the ovary to produce an egg. The growing egg makes a hormone called estrogen. When ovulation occurs and the chosen egg is released, the area in the ovary where the egg originally developed produces a second hormone, progesterone. Hormonal methods of emergency contraception use pills containing derivatives of progesterone and/or estrogen.
These hormones work in one or more of the following ways:
1. Prevent fertilization: After sperm are ejaculated into the vagina, they must travel into the cervix, through the uterus and fallopian tube, before finally reaching the egg (usually near the end of the fallopian tube). Hormones in emergency contraceptives cause the fluid within the cervix to thicken, thereby making it more difficult for sperm to travel along the fallopian tube.
2. Delay ovulation: Successful fertilization requires carefully synchronized timing between the release of the egg from the ovary (ovulation), the presence of sperm nearby to fertilize the egg, and a favorable lining in the uterus for the embryo to implant. The hormones in emergency contraceptives delay or even prevent the release of the egg from the ovary and therefore disrupt the careful timing required for fertilization.
3. Prevention of implantation: After the egg is fertilized in the fallopian tube, it must then travel to the uterus where it will implant in the lining of the uterus. The hormones in emergency contraceptives change the lining of the uterus so that it is less "receptive" to the embryo.
4. Causes the part of the ovary that produces progesterone to regress.
Hormonal forms of emergency contraceptive do not interfere with an embryo that has already implanted nor do they disrupt an ongoing pregnancy.
There are two types of hormonal contraceptives: progesterin-only and estrogen plus progestin combo pills. Historically, emergency contraceptives were administered by taking large doses of birth control pills. Since birth control pills contained estrogen plus progestin, the earliest forms of emergency contraceptives contained high doses of estrogen and progestin, too. However, the estrogen component was found to cause many of the unpleasant side-effects associated with emergency contraception such as nausea and headaches and so progestin-only versions of emergency contraceptives were developed. The progestin-only versions of emergency contraceptive are just as good at preventing pregnancies as the estrogen plus progestin versions and have fewer side effects. They are, therefore, the preferred hormonal version of emergency contraceptive.
Progestin-only emergency contraceptives commonly available include a two-dose regimen and a single-dose regimen. In the two-dose regimen, a pill containing 0.75 mg of levonorgestrel is taken followed by a second 0.75 levonorgestrel pill 12 hour later. In the single-dose regimen, a single tablet containing 1.5 mg of levonorgestrel is taken. Both regimens are available over-the-counter and without a prescription for women 17 years and older but a prescription is required for women younger than 17 years. In both regimens, the medication should be taken as soon as possible but no later than 120 hours after unprotected intercourse. The medications work better the sooner you take them, but in general are 98% effective.
Non-hormonal Emergency Contraception
The second class of emergency contraceptives are non-hormonal contraceptives. These include the copper intrauterine device (IUD) and ulipristal acetate, a medication that blocks the action of progestin.
The Copper intrauterine device is a T-shaped piece of plastic-like material with a copper band along the stem, about the size of a standard paper clip. Your doctor places it into the uterus through the vagina. Unlike hormonal methods of emergency contraception, the IUD is effective up to 5 days after unprotected intercourse. It also has the advantage of being extremely effective (>99.8% efficacy) and lasts up to 10 years (though it can be removed at any time). The IUD works by preventing fertilization.
Ulipristal acetate is a medication that binds to the progesterone receptor and therefore prevents naturally produced progesterone from functioning to support pregnancy. It is effective up to 120 hours after unprotected intercourse. Ulipristal acetate is as effective as Levonorgestrel.
Published On: July 15, 2011