Some birth control less effective for heavy women

A recent review article, which examined the results of seven studies on the success of hormonal contraceptives, concludes that the situation might be more complex. Some birth control methods, such as the pill, might be less effective in obese women, while others, such as those given using a shot, might work just as well.

Adding to the confusion, scientists know little about how extra fat might lead to changes in metabolism and affect the way contraceptives are handled by the body. The researchers call for more studies of birth control in obese and overweight women so health care providers can best advise their patients.

In total, the seven studies included 39,531 women. Four of the studies suggested that the heaviest women have the highest risk of pregnancy while using the contraceptives.

Yet a closer look at the studies, the researchers 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 than those in the normal weight range. But two other studies looking at BMI and pregnancy risk found no such risk. In another study of contraceptive skin patches, higher body weight — not higher BMI — was associated with higher risks of pregnancy.

BMI is thought to be an indicator of how much fat a person has, while body weight reflects the overall body size. So currently, the evidence that extra fat reduces the effectiveness of oral birth control is limited.

Other contraceptives such as injectable or implantable hormones might "be unaffected by body mass," said study author Laureen Lopez, of FHI, a global health and development organization. There was little difference in the rate of pregnancybetween obese and non-obese women who used these methods, according to the studies.

Many researchers think that metabolic changes associated with obesity — in particular, the amount of body fat — could make hormonal birth control less effective. "However, we know little about how overweight women metabolize hormonal contraceptives," said Lopez, "since many studies exclude overweight women."

Women who are obese or overweight also should consider potential health risks from hormonal contraceptives, said Dr. Amitasrigowri Murth, who directs the reproductive choice program at Bellevue Hospital Center in New York.

http://www.msnbc.msn.com/id/38282658/ns/health-diet_and_nutrition/