The findings appear unlikely to boost the popularity of the female condom, whose downsides are already well known, at least to researchers.
"Compared to the male condom, the female condom is more difficult to use and frequent problems are experienced by both partners," says study co-author Dr. Maurizio Macaluso, senior research scientist with the U.S. Centers for Disease Control and Prevention's Division of Reproductive Health.
On the other hand, he says, the female condom remains an option for those who want to reduce the risk of pregnancy. The study found the product worked at least 79 percent of the time, preventing semen from penetrating the female partner and potentially causing pregnancy. The condom also may prevent sexually transmitted diseases (STDs).
Female condoms, which have been available for several years, are made of plastic and inserted into the vagina like a diaphragm. "When it is placed properly, the outer ring keeps the open end of the condom outside of the woman's body and covers some of the external genital parts, while the inner ring anchors the closed end of the condom inside the body," Macaluso says. "The woman can put it in place by herself and ahead of time."
Some women prefer female condoms, but they cost more than male condoms and are harder to find, he says. According to a 1995 survey, just 1 percent of contraceptive users said they use the female condom.
Macaluso and colleagues recruited 210 women in Birmingham, Ala., and told them to use female condoms and take measurements of vaginal fluid both before and after sex. The findings appear in two studies in the Feb. 15 issue of the American Journal of Epidemiology.
Depending on which measurement was used to study the vaginal fluids, the condoms prevented penetration by semen between 79 percent and 93 percent of the time. The researchers didn't compare those numbers to those of male condoms, although they plan to do so later.
Most of the couples experienced at least one mishap related to the female condom. "Many problems were related to the condom moving out of place: for example, the outer ring was pushed in, or the whole condom came out during sex," Macaluso says. "Also, pain or discomfort was often felt by the woman or by the man during sex."
Breakage, however, was extremely rare. Only 15 female condoms broke out of more than 2,200 that were used.
According to Macaluso, 3 percent of American women will become pregnant over one year if they use the male condom every time they have sex; a study found that number is 5 percent among female condom users. On the other hand, the likelihood of pregnancy is 85 percent when no birth control is used.
The new studies found the female condom provided less protection in three types of couples -- those who had been together less than two years, those who engaged in "very active" intercourse, and those who had a "large disparity" between the size of the penis and the size of the vagina.
Dr. Paul D. Blumenthal, an associate professor of gynecology and obstetrics at Johns Hopkins University, is a bit skeptical that vaginal measurements would be valid. "The vagina is an amazingly plastic organ," he says. "I am not sure that if vaginal depth were measured in the clinic, for example, that it would have any meaningful relationship to its width and depth during intercourse."
Blumenthal adds that readers must look at the female condom studies with caution because they examined only how much semen got past the condom, using a measurement of a chemical that is in semen. "It's a good idea, but it's not the same as observing X number of pregnancies or Y number of STDs among users."
Blumenthal says couples who rely on the female condom need to follow directions. "Understand that no method is perfect and that latex has its limits," Blumenthal says. "If the likely established failure rate of 10 to 20 percent is not acceptable to you, then discuss alternative methods with a health professional."
For his part, Macaluso adds that while female condoms may prevent some STDs, the only foolproof prevention methods are abstinence or monogamous sex with a healthy partner.