Mother-to-infant transmission of human immunodeficiency virus (HIV)
occurs, without any intervention, at rates of 14% to 42% in various settings.1,2 Determining the timing of such transmission
is of great clinical relevance for implementing cost-effective prophylaxis.3,4 Based on virologic detection of HIV
during the infant's first 2 days of life, it is generally accepted that about
one third of transmissions in nonbreastfeeding women occur during gestation
and the remaining two thirds during delivery.5-9
Further support for the notion that most HIV transmission occurs intrapartum
includes the association of transmission with prolonged duration of membrane
rupture,10-12
the protective effect of elective cesarean delivery,13-16
and a virologic and immunologic pattern of acute primary HIV infection in
a majority of affected infants.17 However,
these findings could be explained by transmission either very late in gestation
or during labor.