Mechanisms of virus transmission to the fetus. A) ascending transmission to upper reproductive tract. B) transmission through maternal macrophages to the placenta trophoblast. C) transcytosis transmission through attachment to the receptor in the apical surface and ejection to inner layers. D) transmission from maternal vascular endothelium to extravillous trophoblasts (EVTs). Further details can be seen in the article by Heydarifard et al. in this issue.