Objectives: To estimate when mother-to-child transmission occurs and investigate the possible role of maternal factors.
Design: We studied virological data obtained in the first 3 months of life of 95 infected newborns born to HIV-1-seropositive mothers included in the French Prospective Cohort Study who did not breast-feed.
Methods: Comparative Western blot analysis of sequential blood specimens from neonates and mothers with incomplete antibody patterns enabled us to detect antibody production in some infants. The results of viral investigation of neonate specimens enabled us to describe the acute phase of infection in newborns. Because the process between infection and antibody production is irreversible, we chose a Markov modelling technique, which is well suited for staged clinical processes.
Results: About two-thirds (65%) of the infants were considered to have been contaminated during delivery. In the remaining infants, the contamination was estimated to have occurred in utero and 95% of them had been infected less than 59 days before delivery. The association between the mother's immunological and virological status and the time of transmission was examined. The greater the degree of maternal immunodeficiency at delivery (in terms of p24 antigen and Western blot pattern) the higher the risk of in utero transmission, showing that vertical transmission is dependent on the mother's immunological status.
Conclusions: These estimates should be considered when designing strategies to prevent mother-to-child transmission.