The risk of MTCT is significantly increased if the mother has
advanced HIV disease, increased levels of HIV in her bloodstream, or
fewer numbers of the immune system cells-CD4+ T cells-that are the main
targets of HIV.
Other factors that may increase the risk are maternal drug use,
severe inflammation of fetal membranes, or a prolonged period between
membrane rupture and delivery. A study sponsored by NIAID and others
found that HIV-infected women who gave birth more than 4 hours after the
rupture of the fetal membranes were nearly twice as likely to transmit
HIV to their infants, as compared to women who delivered within 4 hours
of membrane rupture.
HIV also may be transmitted from a
nursing mother to her infant. Studies have suggested that breastfeeding
introduces an additional risk of HIV transmission of approximately 10 to
14 percent among women with chronic HIV infection. In developing
countries, an estimated one-third to one-half of all HIV infections are
transmitted through breastfeeding.
WHO recommends that all HIV-infected women be advised about both the
risks and benefits of breastfeeding for their infants so they can make
informed decisions. In countries where safe alternatives to
breastfeeding are readily available and economically feasible, this
alternative should be encouraged. In general, in developing countries
where safe alternatives to breastfeeding are not readily available, the
benefits of breastfeeding in terms of decreased illness and death due to
other infectious diseases greatly outweigh the potential risk of HIV
PREVENTING MOTHER-TO-CHILD TRANSMISSION
In 1994, a landmark
study conducted by the PACTG demonstrated that AZT, given to
HIV-infected women who had very little or no prior antiretroviral
therapy and CD4+ T-cell counts above 200/mm3, reduced the
risk of MTCT by two-thirds, from 25 percent to 8 percent. In the study,
AZT therapy was initiated in the second or third trimester and continued
during labor, and infants were treated for 6 weeks following birth. AZT
produced no serious side effects in mothers or infants. Long-term
follow up of the infants and mothers is ongoing.
A few years later, another PACTG study found that the risk of
transmitting HIV from an HIV-positive mother to her newborn infant could
be reduced to 1.5 percent in those women who received antiretroviral
treatment and appropriate medical and obstetrical care during pregnancy.
Combination therapies have been shown to be beneficial in treating HIV-infected adults, and current guidelines have