Figure 1.

Infant antibody levels over the three possible stages (in utero, perinatally or postpartum) of mother-to-child transmission of HIV-1. During pregnancy, maternal IgG are transmitted to the fetus across the placenta, reaching normal or somewhat exceeding adult levels at term. After birth, the IgG transferred from the mother disappear progressively, while the amount of IgG being produced by the infant continues to increase. In contrast, the placenta is relatively impermeable to Ig of other classes, levels of which are therefore very low in the newborn.