Maternal viral load and vertical transmission of HIV-1: an important factor but not the only one

Objectives: To investigate the association between maternal RNA load, risk of vertical transmission of HIV-1, and other variables. Methods: Plasma or serum samples from mothers of 373 children, enrolled in the prospective European Collaborative Study, were collected around time of delivery, and HIV-RNA quantified using two types of commercial assay. Wome n and children were followed according to a standard protocol. Adjusted odd s ratios (AOR) were calculated to estimate the effect of RNA load and other maternal Factors on vertical transmission. Results: Maternal RNA levels, mode of delivery and gestational age were ind ependently associated with transmission. Vertical transmission increased wi th increasing RNA levels, but there was no threshold below which transmissi on did not occur. The risk was more than double for women with RNA above th e sample specific median [AOR 2.36 (1.23-4.52)]. Elective caesarean section was associated with a substantial and significant decrease in transmission [AOR 0.19 (0.06-0.55)], and delivery before 37 weeks gestation with an inc reased risk [AOR 2.67 (1.33-5.38)]. Elective caesarean section was effectiv e in both subgroups defined by median RNA level [AORs 0.37 (0.08-1.71) and 0.15 (0.03-0.64) below and above median respectively]. The predicted rate o f transmission in a woman with a low RNA load delivering by elective caesar ean section or vaginally after 37 weeks is around 2%, and 11%, respectively . interpretation: Mother-to-child transmission of HIV-1 is multi-factorial; h igh RNA load is an important determinant but clearly not the only one. Inte rventions that target risk factors other than maternal RNA load remain impo rtant.