The so-called morning-after pill can still be effective in preventing pregnancy if taken up to 120 hours after intercourse, two days longer than previously thought, researchers have found.
The extra time could be particularly helpful to women who need more than three days to obtain the pills, particularly those who have unprotected sex on a weekend. Researchers nevertheless stressed that the sooner the "emergency contraception" is taken after unprotected sex, the more effective it will be.
"Even if effectiveness declines ... it seems unreasonable that effectiveness would drop to zero precisely at 72 hours," the study's authors said. "Certainly, even if starting therapy after 72 hours confers less protection than more prompt initiation, some women could still benefit."
The study was published in the current issue of the Journal of Obstetrics and Gynecology.
A longer time period in which to take the pills would benefit women who have difficulty getting appointments with their doctors. Even in California, one of the few states where women can get the pills from a pharmacist without a doctor's prescription, it can be difficult to find a pharmacy that dispenses the pills.
It also could be helpful for rape victims. In 2001, there were 90,000 rapes in the United States, according to the latest Federal Bureau of Investigation statistics. About 5% of those rapes result in pregnancy, according to Charlotte Ellertson, president of the nonprofit Ibis Reproductive Health in Cambridge, Mass. She conducted the study in her previous position as an associate at the Population Council, a nonprofit organization that funds research of reproductive health and population growth.
The emergency contraception -- actually small doses of birth control pills taken after sex -- is thought to work by delaying ovulation, preventing fertilization or inhibiting implantation of a fertilized egg. Sperm can live for up to a week once ejaculated into the vagina. When the woman ovulates is more important than the time that has elapsed since she had unprotected sex; hence, the sooner she takes the pill, the better.
Once the egg is implanted, however, the pill is not believed to affect it or to cause birth defects if the pregnancy is carried to term. The main side effect is nausea. The study involved 111 women who requested emergency contraception between 72 and 120 hours after unprotected sex. It was sponsored by the Population Council in New York..
Researchers compared failure rates for the group with rates among 675 women who started the pills within 72 hours. Taken as directed, pregnancies occurred in 1.9% of those who took it 72 to 120 hours after unprotected intercourse, which wasn't statistically different from the failure rate of 2% in the 72-hour window.
Nevertheless, many women don't know the morning-after pill is available. It is often confused with mifepristone (formerly known as RU-486), which instigates an abortion. In fact, some hospitals do not dispense the morning-after pill, including about 70% of the 45 Catholic hospitals in California, according to Ibis' surveys.
Nor do some hospitals provide it to rape victims, even though California state law mandates that a female victim of sexual assault be provided with post-coital contraception by a physician or health-care provider.
The awareness of the drug could eventually grow. Women's Capital Corp., which makes Plan B, one of the two morning-after pills specifically sold as emergency contraceptives now on the market, in April asked the Food and Drug Administration for approval to sell them over the counter without a prescription.
The other morning-after pill is called Preven, but there are several brands of birth control pills that can work as emergency contraceptives.
Erica Smock, legislative council for the Center for Reproductive Rights, said that the morning-after pill is unlikely to become the main form of birth control for many couples. "People don't realize that many unplanned pregnancies are not the result of a decision not to use birth control, but rather because the condom broke," she said. Some studies showed that two-thirds of unplanned pregnancies occurred among women using birth control.
"Emergency contraception is more expensive and harder to get than other birth control, so women don't count on it as the main form, only backup," Smock said.