Viral infection of the trophoblast: time to take a serious look at its role in abnormal implantation and placentation?

Fragmentary evidence suggests that trophoblast viral infection may play a role in placental dysfunction, leading to complications including spontaneous miscarriage, preeclampsia, fetal growth restriction and preterm birth. Here, we review the mechanisms underlying differentiation and gestational age-dependent infection of trophoblast cells and the consequences of in vitro infection on trophoblast function. The relationship between trophoblast infection by common viruses and pregnancy outcomes is also analyzed. We conclude that there is sufficient evidence linking placental infection by common viruses, including viruses thought to be non-pathogenic or to have low pathogenicity, to indicate that this effect contributes to poor pregnancy outcome.