Experts say the finding, presented Tuesday at the high-profile 14th International AIDS Conference, represents a great success story in the battle to reduce the ravages of the AIDS virus in the United States.
The progress is attributed to increased voluntary HIV counseling and testing of pregnant women and to subsequent anti-AIDS therapy, said one of the study's investigators, Patricia Fleming, a researcher with the U.S. Centers for Disease Control and Prevention.
The study estimated that about 325 American infants were born infected with HIV in 2000, compared with about 1,760 babies in 1991. That translates to a decrease of about 80 percent.
In developing countries where breast-feeding is commonplace, about 30 percent of babies born to HIV positive mothers are infected. In areas where mothers don't tend to breast feed, the rate is about 20 percent.
A similar pattern was seen in the United States before prevention strategies targeting pregnant women were introduced.
In 2000, only 6 percent of the infants born to HIV positive women were born with the virus, the study found.
Researchers said similar prevention programs need to be stepped up in the developing world, where about 700,000 babies were born with HIV last year.
New drugs such as Nevirapine which cost less than $4 a dose and need to be taken only once make the experiences in the United States and Europe within reach of developing countries, experts say.
Adam Coyne of the Elizabeth Glaser Pediatric AIDS foundation, which was not connected with the study, said the U.S. progress reported at the conference has been one of the "great success stories."
However, the CDC researchers warned that HIV infection rates among women are on the rise, which means that eliminating the transmission of the virus from mothers to children will prove increasingly difficult without a cut in the number of women becoming infected.
Between 1991 and 2000, the population of infected mothers surged from 80,000 to as many as 135,500, Fleming said.
According to the CDC, advances in treatment methods have reduced the risk of transmission from 25 percent for untreated HIV mothers to 2 percent for those taking combinations of anti-AIDS drugs.
However, the treatment is far from perfect and improvements in drug therapies appear to be reaching a limit.
Fleming estimated that even with the best antiretroviral treatment, up to 130 infants would be infected each year.
"The simple fact is that the best way to prevent new infections in babies is to prevent infections in women," she said.
Last month, President Bush pledged $500 million to AIDS projects in Africa and the Caribbean that focus on preventing the transmission of HIV/AIDS from mothers to children.