HIV may cause placental infection and subsequently intrauterine infection of fetus. This possibility is supported by the findings that some placental cells express CD4, and the fact that two peaks of HIV positivity can be detected in the infected neonate: Around 40% of the HIV infected infants turned into AIDS patients within 3 years.
Without interventions, the risk of Mother-to-child Transmission (MTCT) varies between 15-40%, depending on factors such as breastfeeding, maternal plasma viral load, clinical status, and the antenatal CD4 T-lymphocyte counts. The maternal plasma viral load is recognised as the strongest predictor of transmission. The use of antiretrovirals and HAART during weeks 14 to 34 of pregnancy can significantly reduce the viral load and thus the risk of MTCT. A combination of interventions (including combination antiretroviral therapy, caesarean section and avoidance of breastfeeding) is associated with a vertical transmission rate of less than 1-2%.
To address the problem of missed diagnosis, From September 2001, all antenatal patients booked in public antenatal clinics (Hospital Authority hospitals and Maternal & Child Health Clinics) are offered free HIV antibody test on top of their usual antenatal blood tests. Prompt diagnosis and intervention is the key to effective MTCT prevention.
MTCT is unique in the sense that a window of opportunity exists whereby appropriate biomedical intervention can prevent the occurrence of the infection. Furthermore, as HIV infected women are enjoying better general health while receiving highly active antiretroviral therapy (HAART), they may be more willing to start a family and rear a child, whereas in the past most would avoid or terminate pregnancy.