Fig. 4. Possible mechanisms of vertical transmission.

The mechanisms by which many TORCH (Toxoplasma gondii, other, rubella virus, cytomegalovirus, herpes simplex virus) pathogens access the fetus are unclear. However, studies suggest that some of these pathogens may use similar pathways to bypass the placental barrier. These mechanisms include infection of extravillous trophoblasts (EVTs; green cells) and/or infection of the maternally derived decidua, such as through direct infection of maternal immune cell populations. Other possible routes include direct infection of transmission across chorionic villi, through direct infection of the syncytium (SYN) or through inflammation-mediated damage of the syncytiotrophoblast layer that disrupts the barrier and allows transmission.