Two separate studies, both backed by the National Institute of Health, have released their results indicating that the amount of human immunodeficiency virus (HIV) a pregnant woman carries in her blood is the single most important factor in determining the risk of passing the virus to her child.
In the first study, The Pediatric AIDS Clinical Trials Group (PACTG) Study, the intent was to see if HIV-positive pregnant women given AZT and immune therapy had fewer infected children than women treated with AZT alone. Babies were tested for HIV at birth, six weeks, six months, and one year. The study had more than 500 participants but was halted early because the transmission rate of HIV was found to be five percent, regardless of the type of treatment.
The second study, The Women and Infants Transmission Study (WITS), was conducted at Northwestern University where researchers tested almost 600 HIV-positive pregnant women to see if the mother's viral load could be used to predict which babies would be HIV-positive. The WITS study did show that a mother with a high viral load is indeed more likely to pass the virus to her child. However, when it came to predicting which babies were most likely to be infected, it didn't seem to matter when in the pregnancy the high viral load occurred.
In the WITS study, 20 percent of the infants were infected with HIV. Some of this study took place before 1994 when AZT became a standard treatment of HIV-positive pregnant women. The rate of infection after 1994 fell to nine percent. Women with high viral loads were three times more likely to have an infected baby. None of the women with a viral load lower than 1,000 copies of HIV RNA per milliliter of blood had HIV-positive babies.
Other individual factors also contributed to the likelihood of perinatal viral transmission including the mother's CD4 and T cells counts; the amount of virus that can be cultured from her blood; and an infection of the chorion, the membrane that surrounds the baby and contains the amniotic fluid.
However, when all factors are examined together, only a high maternal viral load was predictive of which babies were most likely to be infected with HIV.
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