Important note: Information in this article was accurate in 1996. The state of the art may have changed since the publication date.

Reuters NewMedia, Inc. - Wednesday, 27 November 1996 6:20 PM EST

Although women with little or no detectable HIV in their blood have been thought to pose little risk of infection to their fetuses, the new study finds that transmission of the virus is possible even at the earliest stages of HIV infection.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases said that although HIV transmission to the fetus is most likely to occur when a woman has large quantities of HIV in her bloodstream, the new study published in Thursday's issue of The New England Journal of Medicine shows that there appears to be no absolute threshold below which transmission never occurs. In other words, if the mother is known to be infected, there is always a risk that she will transmit the virus to her fetus.

In the study, 7.6% of fetuses whose mothers took AZT in their last trimester of pregnancy were born infected with HIV compared with 22.6% of fetuses whose mothers did not receive AZT, according to Dr. Rhoda S. Sperling, of Mount Sinai School of Medicine in New York.

The study was a follow up to a previous study of pregnant HIV-infected women and their babies published three years ago. The Public Health Service issued guidelines for the use of AZT in pregnant HIV-infected women as a result of the first study.

AZT, also known as zidovudine, was effective at preventing transmission of the virus regardless of the mother's HIV status. Sperling and colleagues theorize that AZT may prevent replication of HIV at the time the infant is exposed to the virus. It is estimated that 50% to 70% of all mother-to-infant transmission of HIV occurs around the time of delivery. Therefore, giving AZT or another antiretroviral during labor and delivery may be an effective way of reducing the high transmission rates in Third World countries where long-term drug therapy -- such as the regimen used in this study -- is not feasible or is too expensive.

In an editorial accompanying the study, Dr. Catherine M. Wilfert, of Duke University Medical Center, said the study adds to a growing body of information that will hopefully lead to optimal prevention of transmission in the United States and the rest of the world.

Prenatal care is another crucial factor in preventing mother-to-infant transmission. In May, federal legislation was passed requiring all states to show a 50% reduction in the number of infant HIV cases by March, 2000.

Other legislations, including the Ryan White Care Act, also require states to develop programs aimed at reducing the number of babies with AIDS. SOURCE: The New England Journal of Medicine (1996;335;1621-1629)
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