Epidemiology

Emergency contraception (EC) refers to methods of preventing pregnancy that are used after sexual intercourse. Circumstances making visits to the emergency department (ED) necessary include rape, contraceptive failure (e.g., condom breakage), and failure to use a contraceptive.

Approximately 50% of women between the ages of 15 and 44 years have had at least one unwanted pregnancy, which amounts to more than 3 million unwanted pregnancies annually in the United States.¹ No contraceptive method is 100% effective, and the failure rates of contraceptives are surprisingly high (Table 129.1).² Because contraceptive failure is so common, most emergency physicians (EPs) will deal with this issue on a regular basis, and they should be aware of the indications and complications of this treatment.

Table 129.1 Failure Rates of Selected Contraceptive Methods Within 1 Year (%)

METHOD	PERFECT USE	TYPICAL USE
Chance	85	85
Combination pill	0.1	5.0
Progestin-only pill	0.5	5.0
Male condom	3.0	14.0
Diaphragm	6.0	20
Spermicide	6.0	26
Periodic abstinence—calendar method	9.0	NA
Hormonal emergency contraception	0.1	3.0
Copper IUD	0.1	NA

IUD, Intrauterine device; NA, not available.

From Kafrissen M, Adashi E. Fertility control: current approaches and global aspects. In: Larsen PR, Kronenberg HM, Melmed S, et al, editors. Williams textbook of endocrinology. 10th ed. Philadelphia: Saunders; 2003. pp. 665–708.

Pathophysiology

The primary mechanism of action of estrogen-progestin EC is inhibition of ovulation. Additional possible contributing mechanisms include thickening of cervical mucus, altered sperm transport, and changes in the endometrial lining.³ Progestin-only methods (levonorgestrel) do not appear to have an effect on the endometrium. Ulipristal is a progesterone receptor modulator, similar to mifepristone. The primary mechanism of these drugs at the EC dose is inhibition of ovulation, although the possibility of an additional affect on uterine implantation cannot be entirely excluded. Once an embryo is implanted in the endometrium, hormonal EC has no effect on a pregnancy and does not cause abortion.⁴

It is important for the EP to understand the mechanism of action of EC to accurately address the concerns of individual patients. According to the definition of the American College of Obstetrics and Gynecology, pregnancy is established at the time of implantation of the embryo in the uterus.⁵ By this definition, hormonal EC drugs are not abortifacients because these medications do not interfere with already established (implanted) pregnancies. However, individual patients may have a different understanding of terms such as conception and abortion than the medical community does. The known facts should be presented to patients simply and clearly so that they will be informed participants in their health care (Table 129.2 and Boxes 129.1 and 129.2).^6,⁷

Table 129.2 Myths and Facts About Emergency Contraception

MYTH	FACT
EC causes a “medical abortion.”	EC has no effect on an established pregnancy, and EC agents are not teratogenic.
	The primary mechanism of action of EC is inhibition of ovulation.
	Estrogen-progestin combination EC may inhibit implantation of a fertilized egg.
If EC is too easily available, women will “abuse” it and use EC instead of regular forms of birth control.	Women who receive advance prescriptions for EC agents are not less likely to use regular forms of birth control.
EC agents contain high doses of hormones and are dangerous to use.	The small dose of hormones in EC agents is extremely safe and can be used by virtually any woman.
EC is readily available in the United States.	Although FDA approval for over-the-counter EC medications is an improvement, availability in EDs, as well as pharmacies, is variable. The emergency physician must be a patient advocate and ensure that the patient is able to obtain the medication that has been prescribed.