"Overweight and on the pill? You might want to try backup contraception."
That was advice issued five years back in U.S. News and World Report, in light of a University of Washington study that found the pill to be less effective in overweight and obese women. Research performed at Oregon Health and Science University in subsequent years seemed to back up the conclusion that heavier women relying on oral contraceptives experienced more unintended pregnancies than did women of healthy weight.
After three or four months of using the oral contraceptives -- the time it usually takes for a woman's body to acclimate to the pill -- the women had multiple ultrasounds and blood tests to determine if ovulation was being suppressed. The goal of oral contraception is to suppress ovulation.
Of the 150 women who used the pill consistently, three of the 96 women with normal weight ovulated, as did one of the 54 women with obesity. The researchers also found that when women were not taking the pill regularly, they ovulated with greater frequency.
"Our findings strengthen the message to patients that the pill will only work if it is taken every day. Weight does not seem to have an impact on suppression of ovulation, but consistency of pill-taking does," [principal investigator Carolyn Westhoff] says.
All women in the study were randomly assigned one of two dosages. Across the board, the lower dose proved just as effective - a significant finding since a higher dose imparts greater risk of developing blood clots.
The study appears in the August edition of the journal Obstetrics & Gynecology.