Men are at a greater risk of contracting HIV when their partner is pregnant and living with the virus, according to a study presented at the 2010 International Microbicides Conference in Pittsburgh.

The study was conducted in Botswana, Kenya, Rwanda, South Africa, Tanzania, Uganda and Zambia.

For up to two years, researchers evaluated more than 3,000 couples in which one partner was HIV positive and the other was not. During the study, 823 pregnancies took place, allowing researchers to understand what circumstances and determinants affect HIV risk.

They found that pregnancy was associated with increased risk in both female-to-male and male-to-female HIV transmission. For women with HIV-positive partners, factors other than pregnancy, such as sexual behavior, contributed to HIV risk.

However, in men, the link between pregnancy and HIV risk was clearer, even after considering whether or not they practiced unprotected sex or were circumcised. In addition, the HIV-positive partner's viral load and CD4 counts had no bearing on transmission.

The increased rate of female-to-male HIV transmission during pregnancy may result from the physiological and immunological changes in women during pregnancy, but more research is needed to confirm this conclusion, said the study authors.