Pregnant women infected with HIV are more likely to spread the virus to their children if they are carrying twins, according to a report in the journal AIDS.

Dr. Laurent Mandelbrot of the University of Paris, and associates investigated mother-to-child spread of HIV in twins, compared with single infants, born to HIV-infected mothers in the French Perinatal HIV Cohort.

Before the advent of highly active antiretroviral therapy (HAART), an effective combination of anti-HIV drugs, the mother-to-child HIV transmission rate in twin pregnancies was two to three times that in singleton pregnancies, the investigators report. Since HAART began in 1997, rates have been similarly low in both groups.

The pre-HAART data indicate that, after adjustment the data for length of pregnancy, delivery method, and other factors, the results indicate that twin pregnancy remained associated with a 2.3-fold increased risk of mother-to-child HIV spread.

The association was particularly strong, the researchers note, in cases of premature rupture of the membranes, a condition in which the sack around the fetus breaks early. In such cases, the risk of mother-to-child HIV spread was increased 4.5-fold.

"In cases of multiple pregnancies in HIV-infected women, (physicians) must take into account the risk of preterm premature rupture of the membranes and preterm delivery," the investigators conclude. "In particular, we would recommend starting effective (anti-HIV) therapy no later than beginning of the second trimester."