New York, Jan 10 (IANS): Using an injectable birth control method may increase the risk of HIV infection in women, a large meta-analysis of 12 studies in sub-Saharan Africa shows.

The hormonal contraceptive, depot medroxyprogesterone acetate, is sold under the brand name Depo-Provera and is administered as a shot every three months.

"The results have potentially broad implications because hormonal contraceptives remain popular for women worldwide," said study lead author Lauren Ralph from University of California, Berkeley.

The findings included data from 39,500 women. The researchers selected the studies based upon methodological rigor, such as whether they accounted for the use of condoms.

In addition to Depo-Provera, the studies also examined other commonly prescribed forms of hormonal contraception.

The other birth control methods did not appear to increase HIV infection risk for women in the general population, the researchers noted.

The study found that women who used depot medroxyprogesterone acetate had a moderate, 40 percent increased risk of acquiring HIV compared with women using non-hormonal methods and those not practicing birth control.

The study found that women who used depot medroxyprogesterone acetate had a moderate, 40 percent increased risk of acquiring HIV compared with women using non-hormonal methods and those not practicing birth control.

The increased risk was slightly lower, 31 percent, among the studies done in women in the general population.

It remains unclear why the increased risk was seen among those using Depo-Provera but not the other forms of hormonal contraception, the authors noted.

One possibility may be that birth control with higher levels of progestin, the synthetic form of the natural hormone progesterone, changed the vaginal lining or altered local immunity, increasing the risk for HIV infection, they added.

The findings appeared in the journal Lancet Infectious Diseases.