B. Joyce Simpson and colleagues at Yale University reported that, among mothers infected with HIV-1, treatment with orally administered zidovudine alone, in the course of routine prenatal care is associated with a significant reduction in the risk of vertical transmission. The decline in transmission was most dramatic among women with the lowest CD4+ T-lymphocyte counts.
The researchers noted an "abrupt decline" of vertical HIV transmission in 1990 in a prospectively followed cohort of 267 infants of HIV-positive mothers. This led them to perform a retrospective, observational study to identify factors that caused the decrease. Specifically, they evaluated the impact of orally administered zidovudine, CD4+ T-lymphocyte count and mode of delivery.
The team found that the risk of transmission was 18.6% in infants of all women not treated with zidovudine compared with 5.5% in infants of all women who were treated. In particular, among the subset of women with CD4+ cell counts below 200/microliters who received zidovudine, they found the risk of vertical HIV transmission decreased nine times. They also noted an inverse relationship between risk of transmission and CD4+ cell count, but found no significant association between mode of delivery and vertical transmission of HIV.
After adjusting for potential confounding factors, the relationship between maternal zidovudine treatment and decreased risk of vertical HIV transmission remained "robust" and "strong." They believe these results provide further support for the effort to encourage widespread, perhaps universal, education and counseling about HIV infection and to offer all women of childbearing age an opportunity to be tested for HIV.
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