The new pills, if taken properly, probably work as well as the old pills in most healthy women, according to Dr. Charles Lockwood of Yale University, acting chairman of the FDA panel. However, pregnancy rates do seem to be higher in women using the new generation of lower-estrogen birth-control pills. In clinical trials over the last decade, two out of every hundred women have gotten pregnant on some of the new pills, compared to one out of every hundred on the old higher-estrogen pills. If those numbers are true for women as a whole, it would mean that the new pills have twice the failure rate of the old ones. The most likely cause? The obesity epidemic, says Lockwood. So, to add to the long list of health complications that come with being overweight, it seems, some women can now add unplanned pregnancy.
The reason new pills may not be working as well for heavier women is something doctors call “forgiveness.” All birth-control pills work by raising the body’s levels of female hormones, which tricks it into not ovulating. The next-generation of hormonal birth-control methods—including patches such as Ortho Evra, as well as pills such as Seasonale and Ortho Tri-Cyclen Lo, typically contain lower levels of hormones than the versions developed decades ago. The reduced level of hormones in the new pills helps reduce some side effects, but it also means they are less forgiving should a woman miss a day or two. And unlike some drugs, birth- control pills aren’t prescribed according to weight—obese and overweight women get the same doses as their slimmer counterparts. But their bodies don’t react the same way. “It’s one thing to forget a low-dose pill if you’re 5-foot-3 and you weigh 100 pounds,” says Lockwood. “But boy, it’s another if you’re the same height and you weigh 200 pounds.” In heavy women, the chemicals must literally cover a larger area, and they’re metabolized faster. If these women accidentally skip a low-estrogen pill, they’re less likely to be protected by any leftover hormones from the previous day. A low-dose pill that is 99 percent effective in thin women who take it every day, then, may be less so in larger women who forget it every once in a while. Overweight women on the pill may have as much as a 60 percent greater risk of getting pregnant, according to a 2004 study in the journal Obstetrics & Gynecology.
Carol Cox of Barr Pharmaceuticals says she is “not aware that the women in Barr’s trials were any different” than the women she’d expect to use the company’s popular pill Seasonale, and that “weight was not an issue” in the trial of that drug. “We certainly want products to be effective and safe, and we believe our products have been. But we look forward to having these forums with the FDA and we’re open to continuing dialogue,” she says. (Ortho-McNeil did not return calls seeking comment.)
Given these issues, the FDA’s panel recommended that the agency look closely at drug-company studies to ensure that the participating women are an accurate reflection of average American women—not skinnier, younger, and healthier than the general population. “We don’t want people to cherry-pick the participants in the study to make their drug look good,” says Lockwood. Trials from the past decade were conducted along those lines and may therefore be flawed by today’s standards. “The exclusionary criteria for those trials were probably set a long time ago, when people weren’t as heavy,” says Natalie de Vane, a spokeswoman for Wyeth Pharmaceuticals. Some new trials are already starting to take the rising rates of obesity into account. The FDA is currently considering a new Wyeth drug, Lybrel, which de Vane says was tested in “a broad base of patients,” including heavier women. The panel also suggested several other ways that studies of birth-control pills could be improved: better record-keeping, for instance, and smarter follow-up studies.
What the panel didn’t do, though, was recommend a limit for the percentage of unintended pregnancies that would be acceptable in birth-control pills. (The FDA has no limit now; efficacy data based on their own studies is provided by drug companies within individual packs of pills and is thought to be about 98 percent.) “The FDA really wanted us to say something like, ‘you have to have a failure rate of less than 2 percent.’ But all the other changes we recommended [about how studies should be conducted] meant the numbers we have might not be real,” says Lockwood. The studies that have been done so far may be misleading—and the true efficacy rates of existing birth control aren’t known for sure, he explains.
It’s also possible that the rise in pregnancy rates for women on the pill reflect improvements in pregnancy tests. “Over the last 30 years our ability to detect a pregnancy early has improved,” says Kirsten Moore, president of the Reproductive Health Technologies Project, a nonprofit advocacy group. Pregnancies that might have ended early in miscarriage—and not have been included in previous statistics—might be tallied in more recent counts.
Despite the decline in effectiveness, the FDA’s panel did not recommend that the new low-estrogen pills be restricted or removed from the market. Part of the reason they were reluctant to do so was because the new pills have other benefits that might be worth the trade-off for some consumers who are advised to make the choice in consultation with their doctor. Not only do the low-estrogen pills carry less risk of dangerous cardiovascular problems such as heart attacks and strokes, but some women find that they have fewer mild side effects, such as weight gain and a darker mood. And while women usually use the pill for birth control, some take it to battle acne or regulate their periods. “Most women can expect to be using birth control for about 30 years,” says Moore. “Given that length of time, her body’s going to change, and so is her lifestyle. Our focus should be on maximizing the chance that she finds the right pill for her at all points in her life.”
Whichever pill a woman chooses, she’ll likely want to know what her chances are of getting pregnant. One thing is for sure, her odds are better on the pill than just with condoms—which may have a failure rate of up to 14 percent. But until the studies are refined and there is more definitive data on effectiveness rates, accurate numbers may be hard to come by. In the meantime, the 12 million women who rely on the pill for birth control should be especially careful about taking their daily dose.
