Birth Control Pills Just As Effective For Obese Women
Despite previous studies suggesting otherwise, a new study suggests that birth control pills work just as well to prevent pregnancy in obese women as it does in thinner women.
Dr. Carolyn L. Westhoff of Columbia University Medical Center in New York and her colleagues found that as long as a woman — no matter the size — took the pill consistently, it prevented her ovaries from producing eggs.
Reuters reports that previous studies have found that obese women are as much as 40 percent more likely to get pregnant while taking the pill than normal-weight women, possibly because excess weight may weaken the effectiveness of the pill.
In Westhoff’s study, the team enrolled 226 normal-weight or obese women, randomly assigning them to take a lower or higher dose of the pill. After three or four cycles of oral contraceptives, the researchers then had the women undergo ultrasounds and blood tests to determine if their ovaries were making eggs.
The researchers also tested women’s blood levels several times to determine if they were using the pill consistently. About 90 percent of the normal weight group had hormone levels that indicated consistent use, compared to 72 percent of obese women.
Of the 150 consistent pill users, 97 percent did not ovulate, meaning they would not have gotten pregnant during that cycle. Whether or not a woman was obese didn’t affect her likelihood of ovulation. Among the consistent pill users, three of the 96 normal-weight women ovulated, and one of the 54 obese women did.
More than a third of the 13 women who were inconsistent pill users ovulated, and two-thirds of the 18 non-users produced eggs.
The new findings should lay to rest concerns that obese women are more likely to get pregnant while on the pill, Westhoff told Reuters.
The issue has baffled doctors because some companies have pushed physicians to prescribe higher dose formulations to their obese patients based on the idea that lower doses are not effective, Westhoff noted.
Obese women are at increased risk of developing life-threatening blood clots in the veins and taking higher doses further increases the risk of blood clots.
Westhoff says, according to their findings, obese women should be reassured that lower doses will be effective in preventing pregnancy.
The trouble with previous studies was that women were asked to recall unintended pregnancies that had occurred in the past, reporting their own weights, rather than being weighed by the research team, Westhoff told Reuters.
Dr. Victoria Holt of the University of Washington in Seattle, who led studies finding different failure rates among obese and normal-weight women, told Reuters she still believes obese women are more at risk of becoming pregnant while on the pill.
She argues that Westhoff’s research suggests obese women are less likely to achieve adequate hormone levels while taking the pill, because just 72 percent had levels indicating consistent oral contraceptive use, compared to 90 percent of the normal-weight women.
The National Institutes of Health will assemble a group of experts this November to investigate whether further research is needed on obesity and oral contraceptives. The Food and Drug Administration is also planning a hearing to address evidence that a new emergency contraceptive pill is more likely to fail in obese women.
Dr. James Trussell, the director of the Office of Population Research at Princeton University in New Jersey, todl the new agency, “It’s a particular concern in the United States because obesity is increasing so rapidly.”
“I would say that the pill is still not going to be the front line, the top tier contraception for obese women,” he added.
Methods with a lower risk of failure due to human error, like the IUD, hormonal implants, or vasectomy for the male partner, would likely be a better choice, he said.
Westhoff and her colleagues report their findings in the August issue of Obstetrics & Gynecology.
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