Current Issues in Emergency Contraception: An Overview for Providers

Jennifer Brunton, CNM, MSN; Margaret W. Beal, CNM, PhD

Disclosures

J Midwifery Womens Health. 2006;51(6):457-463. 

In This Article

Background

Oral Contraceptive Pills and Their Use as Emergency Contraception

Hormonal birth control pills were first approved by the US Food and Drug Administration (FDA) in 1960. In 1966, Morris and Van Wagenen[4] demonstrated that large doses of estrogen were effective in preventing pregnancy after unprotected intercourse, and this treatment was used for pregnancy prevention in instances of rape. High rates of gastrointestinal side effects limited the widespread use of this method.

In 1977, Yuzpe published his study on the use of combined OCPs for post-coital contraception, and this method became the new standard.[5] The addition of progestin allowed for a smaller dose of estrogen, which reduced side effects without compromising efficacy. The Yuzpe regimen consists of two doses of 0.1 mg ethinyl estradiol and 1.0 mg of dl-norgestrel taken 12 hours apart. Although newer treatment regimens have been developed, the Yuzpe regimen is still used today and includes "off-label" treatment with combined oral contraceptives. The Yupze regimen is FDA-approved, and there are many OCPs that have been declared safe and effective for use as EC. Table 1 includes a partial listing; additional generic equivalencies can be verified by comparing doses or consulting a comprehensive source such as Hatcher's Contraceptive Technology.[6] Oral contraceptives containing the progestin norethindrone have been shown to be safe but less effective than those formulated with norgestrel and levonorgestrel.[6,7,8]

Progestin-only Pills

The use of progestins alone for EC was first proposed in 1973. The original idea was that progestin-only pills could be taken after each act of intercourse, eliminating the need for daily dosing and continuous hormonal exposure. This form of intermittent contraception (dubbed "vacation pills") was available in several countries under the trade name Postinor, but was not widely adopted because of lower efficacy than other available forms of contraception. Although the original Postinor is no longer available, a progestin-only EC product named Postinor 2 (Schering [NZ] Ltd.; Albany, Auckland, New Zealand) is available outside the United States and via the internet.[9,10]

Although not very effective when used for intermittent contraception, progestin-only OCPs did prove effective for one-time or occasional use as EC. The disadvantage in adopting progestin-only OCPs for this use is the large number of pills that must be taken at once for an effective dose. This led to the development of a product with a higher progestin dose especially marketed for use as EC.[11] Table 2 includes information on the hormonal content of selected progestin-only ECPs.

Preven and Plan B

In September 1998, the FDA approved the application of Gynetics, Inc. (Belle Mead, NJ) to market Preven, the country's first dedicated EC product. The Preven regimen consisted of four combined hormonal pills, each containing 0.1 mg of ethinyl estradiol and 0.5 mg of levonorgestrel. The package contained a urine pregnancy test, instructions, and 4 pills to be taken two at a time, 12 hours apart.[6,12]

In July 1999, the FDA approved Plan B, the second dedicated EC product. Now produced by Barr Pharmaceuticals (Woodcliff Lake, NJ), Plan B is a progestin-only medication that consists of 2 pills, each containing 750 mcg of levonorgestrel. The regimen not only requires fewer pills than the Preven regimen (2 pills with Plan B, as opposed to Preven's 4), but has been shown to have similar efficacy with fewer side effects.[6,12,13]

Although Preven is still considered safe and effective, it was withdrawn from the market in 2004 because of the high demand for Plan B.[14]

The Copper Intrauterine Device

Postcoital insertion of a copper IUD for EC was first reported in the literature in 1976.[15] The copper IUD is 94% to 99% effective at preventing pregnancy when inserted up to 120 hours after unprotected intercourse.[6,16] Although it is not cost-effective when used only for EC, it can be left in place for the usual 10-year period. This method is more widely used outside of the United States, where IUD insertion is cheaper and has greater acceptance. The levonorgestrel-releasing intrauterine system (Mirena; Berlex, Wayne, NJ) is not approved for use as EC.[6,12]

Mechanism of Action

There is no evidence that use of progestin-only pills or Plan B prevents implantation of a fertilized ovum, although postfertilization effects may contribute to the efficacy of the Yuzpe method. For those who believe that life begins at the time of fertilization, the possibility that EC acts to prevent implantation of a fertilized egg presents an ethical dilemma. The literature clearly shows that progestin-only emergency contraceptive pills act before fertilization to inhibit, delay, or blunt the luteinizing hormone surge or to inhibit follicle rupture, thereby inhibiting or delaying ovulation. Levonorgestrel was found to have no direct effect on either endometrial receptors or endometrial development, nor did it affect sperm transport or receptors in the fallopian tubes.[17]

Animal studies also support the hypothesis that levonorgestrel ECPs have their effect before fertilization rather than after. In one study, high-dose levonorgestrel given to rats after intercourse showed total or partial inhibition of ovulation and no effect on fertilization or implantation when administered shortly before or after mating. Studies of cebus monkeys also indicated inhibition of ovulation if given in the follicular phase.[18,19]

A review of 8 studies of the Yuzpe regimen has demonstrated that women using the method in the first half of the menstrual cycle experienced higher efficacy (81%) than those using it after midcycle (17%). This supports the hypothesis that ECPs work primarily by inhibition of ovulation and not by postfertilization mechanisms. However, another statistical analysis showed that inhibition of ovulation is unlikely to be the sole mechanism of action for this regimen. Other proposed mechanisms include corpus luteum function interference; sperm trapping via thickening of cervical mucus; interference with sperm, egg, or embryo transport; or direct inhibition of fertilization.[20,21]

The primary mechanism of action of the copper IUD is to work as a spermicide to prevent fertilization if inserted days prior to ovulation. The copper IUD can also function to prevent implantation by causing an inflammatory response of the endometrium. The IUD does not act as an abortifacient and does not disrupt an already implanted embryo. However, it is not cost-effective to insert an IUD in a woman presenting with unprotected intercourse since the last menstrual period if a pregnancy may be too recently established to be detected by a pregnancy test.[6,16] If a woman's history suggests the potential for an early, established pregnancy, then prescribing ECPs is a better alternative.

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