The largest, most comprehensive study of its kind made by the National Institute of Child Health and Human Development of the National Institutes of Health concluded that hormonal contraception does not seem to increase women's overall risk of infection with the AIDS virus.
Although hormonal contraception provides an effective means of pregnancy prevention, it does not protect against HIV or other sexually transmitted infections.
"Abstinence is the only sure way to prevent sexual transmission of HIV," said H. Trent MacKay, M.D., M.P.H, Chief of the Contraception and Reproductive Health Branch.
Abstinence, use of a latex condom, consistently and correctly, is highly effective against HIV infection. Hormonal contraception is used by more than 100 million women around the world. In all, 18 million women have been infected with HIV, most during heterosexual relations. "Understanding whether hormonal contraceptive use alters the risk of HIV acquisition among women is a critical public health issue".
Many previous studies have considered the issue of whether contraceptives might increase a woman's risk of becoming infected with HIV but the current study was commissioned to overcome many of their limitations.
It was conducted primarily among women seeking family planning services (rather than among high-risk women such as sex workers) who more closely resemble the vast majority of women using hormonal contraception worldwide.
The study was made in Africa and Asia because those parts of the world had a very high incidence of HIV infection.
Comparatively fewer new cases of HIV infection in the United States would have made any U.S.-based study far longer to provide results.
The researchers primarily recruited women at family planning clinics in Uganda, Zimbabwe, and Thailand, ranging in age from 18 to 35 years and were not infected with HIV at the time they were recruited.
At the time they entered in the study, the women were either using no hormonal contraception, or had used oral contraceptives or DMPA for at least three months before the study began.
Women who were not using hormonal contraception used alternative methods as condoms alone, diaphragms and spermicides, sterilization, withdrawal, or periodic abstinence (the rhythm method), or used no method of contraception.
Women seeking care were offered their choice of contraceptive methods, either oral contraceptives or DMPA, as well as condoms.
The women were given instructions on how to use contraceptive methods and how to reduce their risks of becoming infected with HIV.
6,109 women participated in the study: 2,235 in Uganda; 2,296 in Zimbabwe; and 1,578 in Thailand.
They were checked for HIV four to five times a year, for 15 to 24 months.
By the time the study had ended, 213 African women had tested positive for HIV.
In contrast, only four Thai women had become HIV-infected, primarily because the Thai government mandated the use of condoms in the country's brothels during the 1990s, greatly reducing the heterosexual spread of HIV.
The very few cases in Thailand were statistically invalid, so the Thai cases were excluded.
In the 213 African HIV cases all together, no evidence that use of hormonal contraceptives increased a woman's chances of becoming infected with HIV was found.
"There was no statistically significant difference in the risk of HIV acquisition between users of combined oral contraceptives or DMPA and women not using hormonal contraception," said Dr. Morrison.
The study could not rule out an increase in risk for HIV infection among those already at higher than normal risk of acquiring HIV-sex workers.
The study results were "not inconsistent with" a modest increase in risk for HIV infection associated with hormonal contraceptive methods, particularly for DMPA, seen in a study among high risk women in Kenya.
Women with genital herpes did not have an increased risk of acquiring HIV due to hormonal contraception.
But hormonal contraception did increase their risk of acquiring HIV compared with the women who did not have herpes at enrollment and who did not use hormonal contraception.
There was no explanation found.
Previous studies have showed that genital herpes was a risk factor for acquiring HIV.
"In summary, this large, multi-site study found no overall increased risk of HIV acquisition associated with hormonal contraceptive use".
"This provides reassurance for women in moderate and high HIV prevalence settings who need effective contraception that any increased overall risk associated with hormonal contraception is, at most, modest."