Compared with women of normal weight, women who are overweight or obese are more likely to become pregnant while taking birth control pills. A study published in Obstetrics and Gynecology showed that 5% of overweight women (compared with 3% of normal weight women) became pregnant each year while on the pill.
According to researchers, the higher a woman's BMI (body mass index--a relationship of height and weight), the greater her risk is of becoming pregnant while on the pill.
One more reason to get fit this year! By losing just 5 or 10 pounds, you can significantly reduce your risk of an unintended pregnancy. Women with the lowest risk in this study weighed less than 165 pounds. By burning 500 calories per day (through diet and exercise) you can lose about 1-2 pounds a week.