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.