QUANTITATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 DURING PREGNANCY - RELATIONSHIP OF VIRAL TITER TO MOTHER-TO-CHILD TRANSMISSION AND STABILITY OF VIRAL LOAD

To develop strategies to prevent mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1), it is important to define the factors determining it. We examined the relationship between maternal HIV-1 titer and the occurrence of mother-to-child transmission. In add ition, we quantitated HIV-1 longitudinally in mothers during pregnancy , at delivery, and up to 1 year postpartum. To examine transmission, w e prospectively studied 19 mother-child pairs; in 5 pairs, HIV-1 trans mission occurred. We used endpoint dilution culture of peripheral bloo d mononuclear cells to determine maternal viral titer and found that a lthough 4 of 6 (67%) women with viral titers of greater than or equal to 125 HIV-1 infectious units per 10(6) cells transmitted HIV-1 to the ir infants, only 1 of 13 (7.6%) women with lower viral titers transmit ted (P = 0.01). Twelve of the 19 mothers had HIV-1 loads determined se rially 3-8 times over periods ranging from 18 to 65 weeks. Viral titer s varied greatly between the 12 women, but the viral load in each woma n remained stable over time. In this cohort, HIV-1 viral load remained stable during pregnancy and the greater the maternal viral burden, th e more likely that transmission occurred. These two related findings s uggest that determination of HIV-1 titers early in pregnancy may predi ct which women are at high risk of transmitting to their infants and m ay be used to counsel HIV-1-infected women of childbearing age, These data identify maternal viral titer as a major determinant of mother-to -child HIV-1 transmission and thereby provide the scientific rationale for therapeutic strategies designed to interrupt transmission by lowe ring viral load.