Varicella zoster virus (VZV) infection can be serious for pregnant women and their babies, although it is rare. The implications of primary VZV infection vary with the gestational age at infection. For the mother, the risk of severe illness is greatest after mid-pregnancy, when she is relatively immunocompromised. For the fetus, the risk of congenital infection is greatest when maternal infection occurs in the first or second trimester. Maternal infection is preventable by preconception vaccination.