Long-term, progestin-releasing contraceptives - such as IUDs and skin implants - have a negative impact on metabolic markers, which increases a woman's risk of Type 2 diabetes, University of Southern California researchers found.

"Contraceptive studies often only look at normal-weight women," researcher Penina Segall-Gutierrez said in a statement. "Studies such as this are necessary because, today, one-third of women in the US are overweight and one-third are obese. All women, including overweight and obese women, need to have access to safe and effective contraception."

Regular IUDs are safer than implants, the study found. But non-hormonal methods like condoms and copper IUDs are safest of all.

The study, published in the journal Contraception, only looked at obese women, and didn't include other progestin-releasing birth controls like the pill, the ring or shots.