Rates of mother-to-child transmission
Estimates of the rate of mother-to-child transmission of HIV in
cohorts of women who have not received any preventive treatment (such as
antiretrovirals) range from 15-25% in industrialized countries to 25-45% in
developing countries (Msellati et al., 1995). The highest rates of
MTCT have been found in women in Africa (Kind et al., 1998; Maguire et
al., 1997; Ometto et al., 1995; Lallemant, Le Coeur et al.,
1994; Roques et al., 1993; European Collaborative Study, 1992; Blanche
et al., 1989).
Differences in study methods, the composition of the populations
studied, and the prevalence of co-factors of transmission may explain some of
these differences. However, it is likely that much of the increased rate
of transmission seen in women in sub-Saharan Africa is associated with
breastfeeding,1 where many women breastfeed for about 2 years (The
Working Group on Mother-to-Child Transmission, 1995; Ryder and Behets, 1994;
Dabis et al., 1993).
1 Many women who breastfeed do not
breastfeed exclusively. Other fluids (juices, milks, teas) and foods may
also be given to the infant. In many studies looking at HIV
transmission and breastfeeding no differentiation is made between women who
"exclusively" or "partially" breastfeed. In this document, unless
otherwise stated, "breastfeeding women" will often include both women who
"exclusively" or "partially" breastfeed.
In an attempt to quantify the relative contribution of
intrauterine and intrapartum transmission of HIV in non-breastfed
infants, a working definition of timing has been proposed (Bryson
et al., 1992).
In utero infection. In this, a child is classified
as having been infected during pregnancy (in utero) if HIV-1 genome is detected
within 48 hours of delivery by polymerase chain-reaction test (DNA-PCR) or viral
Intrapartum infection. Acquisition of infection is
assumed to have occurred during delivery (intrapartum) if these diagnostic tests
were negative in a sample taken during the first 48 hours after delivery, but
became positive in subsequent samples taken within 7-90 days of delivery.
Following this classification, a French study estimated that of
the infants infected with HIV, 35% of the non-breastfed infants studied were
infected before birth and 65% were infected late in pregnancy or during delivery
(Rouzioux et al., 1995). A recent review indicated that in women
who did not breastfeed their infants, about one-third of MTCT infection was
acquired during the intrauterine period. In women who did breastfeed
their infants, less than a quarter of all MTCT was acquired during the
intrauterine period (Newell, 1998).
Table 1. Percentage HIV infection acquired by different
Partially breastfed/breastfed infants
During intrauterine period
Postpartum, by breastfeeding
*These rates are observed in the absence of
interventions to reduce