The number of babies who got AIDS from their mothers dropped by two-thirds between 1992 and 1997, largely because of prenatal treatment with the drug AZT, a study found.
An expert who was not involved in the study said it suggests the possibility of virtually eliminating mother-to-child HIV transmission in the United States, an idea that was almost unimaginable a few years ago.
"This is a remarkable success story for . . . everybody involved in caring for these women and the women themselves," said the study's lead author, Dr. Mary Lou Lindegren, an epidemiologist with the federal Centers for Disease Control and Prevention in Atlanta.
"We still have more to go, but we've been dramatically successful."
The number of babies who developed AIDS after being infected with HIV before or during birth peaked at 907 in 1992, then declined 67 percent over the next five years, to 297 in 1997, the researchers reported in today's Journal of the American Medical Association.
The researchers think the number of babies born HIV-infected is higher, since it can take years for HIV to develop into AIDS.
Only 32 states collect information on HIV infection in newborns, but the CDC estimates that 1,650 babies caught the virus from their mothers in 1991, at the epidemic's peak. By 1996, that number had fallen to 480, a 71 percent drop, Lindegren said.
Scientists discovered in 1994 that treatment with AZT, now called zidovudine, reduced a newborn's risk of catching HIV from 26 percent to 8 percent.
In that study, the drug was given to HIV-infected women during pregnancy and labor and to the newborn for the first six weeks of life, said Dr. Lynne Mofenson of the National Institute of Child Health and Human Development.
Since then, doctors have found that prenatal AZT can actually reduce the risk to as low as 3 percent, Mofenson said in an editorial accompanying the study. Delivering at-risk babies by Caesarean section lowers the risk further, she said.
Also, if women are getting treatment with powerful AIDS-fighting drug regimens that can reduce virus levels in the blood to undetectable amounts, the risk may fall to less than 1 percent, she said, citing other research.
That means virtual elimination of mother-to-child transmission in the United States looks possible, Mofenson said.
Authors of the study said zidovudine is the main reason for the drop in AIDS cases in newborns, but not the only one.
One other factor is that the number of babies born to infected women fell 17 percent during the study period.