A just-published systematic review of 42 studies in 6 countries over a period of more than 30 years yielded similar results: Among more than 7000 women who had the IUDs inserted after unprotected intercourse, the pregnancy rate was 0.09%.11
But an IUD is appropriate only for women who want long-term contraception and would otherwise qualify for IUD insertion. By comparison, hormonal EC is not as effective and generally works best when used within a shorter time frame.
Progestin alone vs estrogen-progestin combo. To compare hormonal contraception, many researchers use a “prevented fraction”—an estimated percentage of pregnancies averted by treatment. A large World Health Organization-sponsored study found that the efficacy of progestin-only EC is superior to that of the estrogen-progestin combination, with prevented fractions of 85% and 57%, respectively. The progestin-only EC was also associated with significantly fewer adverse effects.12
In more recent studies, the prevented fraction for progestin-only EC has been found to range from 60% to 94%, while a meta-analysis of studies assessing estrogen-progestin EC r evealed a prevented fraction of ≥74%.2
Although there is evidence suggesting that progestin-only EC may work for up to 5 days,13,14 it has FDA approval only for use within 72 hours of intercourse.13 A time-sensitive analysis showed that when it was used within 12 hours of intercourse, the pregnancy rate was 0.5%. The rate increased steadily to 4.1% when the progestin-based EC was taken 61 to 72 hours after intercourse, and rose by an additional 50% after an additional 12-hour delay.15
Hormonal EC is only effective before ovulation occurs. Once luteinizing hormone (LH) starts to rise, it is ineffective. However, the likelihood of pregnancy drops precipitously after ovulation, and there is no risk of pregnancy in the luteal phase, with or without EC.
One pill or 2? Both Plan B and the generic Next Choice are sold as 2-dose regimens, with one 0.75-mg tablet taken within 72 hours and the second taken 12 hours later. Plan B One-Step, which consists of a single 1.5-mg tablet, is clinically equivalent to the 2-dose formula,16 but is more convenient and may improve adherence. Notably, though, one large randomized controlled trial (RCT) in China found that the 2-pill regimen was significantly more effective in preventing pregnancy in women who had further acts of unprotected intercourse after treatment.17
UPA has a 5-day window. UPA has FDA approval for use within 120 hours of unprotected intercourse and has been found to be more effective than progestin-only EC, especially when used on Day 4 or 5 (72-120 hours).8 Adverse effects are mild to moderate, similar to those of LNG, and may include headache, abdominal pain, nausea, dysmenorrhea, fatigue, and dizziness.8
The medication binds to progesterone receptors, acting as an antagonist as well as a partial agonist. The mechanism of action depends on the phase of the woman’s cycle. Taken during the midfollicular phase, UPA inhibits follicle development.18 When used in the advanced follicular phase, just prior to ovulation, it delays LH peak and postpones ovulation.19
In one small study in which women were randomized to either UPA or placebo, researchers found that the drug delayed ovulation for ≥5 days in about 60% of those who took it; in comparison, ovulation occurred by Day 5 in every woman in the placebo group.19
How accessible is EC?
EC has a tumultuous history in the United States,20 and accessibility depends on a variety of factors—age among them.
Plan B, for instance, is subject to a 2-tier system. It was approved in 1999 as a prescription-only product and has been available over the counter (OTC) to women 17 years and older since 2009. Younger women can get it only by prescription.21
Nonetheless, Plan B made the news again last year, when US Health and Human Services Secretary Kathleen Sebelius overruled an FDA decision to give teens younger than 17 OTC access.22 Thus, the age restriction remains in place, although there is no medical evidence to support it.23 Other forms of EC, including UPA, are available to all women only by prescription.
Accessibility of EC also may vary from one part of the country to another. Some states have enacted laws with conscience clauses that allow pharmacists to refuse to dispense EC. Others have worked to increase access by authorizing pharmacists to initiate and dispense EC on their own, provided they work in collaboration with a doctor or other licensed prescriber. As of 2011, 9 states—Alaska, California, Hawaii, Maine, Massachusetts, New Hampshire, New Mexico, Vermont, and Washington—had such agreements in place.24