Maternal levels of plasma human immunodeficiency virus type 1 RNA and the risk of perinatal transmission

Background The importance of plasma levels of human immunodeficiency virus type 1 (HIV-1) RNA in pregnant women in relation to the other factors known to influence the risk of transmission of infection to their infants is inc ompletely defined. We studied the relation of maternal plasma HIV-1 RNA lev els to the risk of perinatal transmission and the timing of transmission. Methods We measured plasma HIV-1 RNA serially in 552 women with HIV-1 infec tion who had singleton pregnancies. The status of infection in their infant s was assessed by culture of blood and further classified as early (if a cu lture of blood obtained within the first two days of life was positive) or late (if a culture of blood obtained in the first seven days of life was ne gative but subsequent cultures were positive). The rates of transmission at various levels of maternal plasma HIV-1 RNA were analyzed by tests for tre nd, with adjustment for covariates by stratification and logistic regressio n. Results Increasing geometric mean levels of plasma HIV-1 RNA were associate d with increasing rates of transmission: the rate was 0 percent among women with less than 1000 copies per milliliter (0 of 57), 16.6 percent among wo men with 1000 to 10,000 copies per milliliter (32 of 193), 21.3 percent amo ng women with 10,001 to 50,000 copies per milliliter (39 of 183), 30.9 perc ent among women with 50,001 to 100,000 copies per milliliter (17 of 54), an d 40.6 percent among women with more than 100,000 copies per milliliter (26 of 64, P<0.001). The treatment status of one woman was unknown. The highes t rate of transmission was among women whose plasma HIV-1 RNA levels exceed ed 100,000 copies per milliliter and who had not received zidovudine (19 of 30 women, 63.3 percent). Neither higher HIV-1 RNA levels early in pregnanc y nor higher levels late in pregnancy were associated with the timing of in fection in the infants. Conclusions In pregnant women with HIV-1 infection, the level of plasma HIV -1 RNA predicts the risk but not the timing of transmission of HIV-1 to the ir infants. (N Engl J Med 1999;341:394-402.) (C) 1999, Massachusetts Medica l Society.