Hormonal contraceptives have had mixed results among overweight women, reveals a new study.
Four of seven studies examined in a recent research review comprising 39,531 women suggest that the heaviest women have the highest risk of pregnancy while using the contraceptives.
Yet a closer look at the studies, the review authors say, reveals a more complicated picture.
In one study of oral contraceptive pills, women with a body mass index (BMI) in the overweight range (a BMI of 25 or more) had a higher risk of pregnancy that those in the normal weight range.
In another study of contraceptive skin patches, higher body weight - not higher BMI - was associated with higher risks of pregnancy.
Other contraceptives such as injectable or implantable hormones might "be unaffected by body mass," said lead author Laureen Lopez, of FHI, global health and development organization.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration.