If a pregnant woman is infected during the first trimester (risk extends to 20th week), a fetus has a 1% chance of developing widespread scarring, hypoplastic limbs, cataracts and brain lesions (congenital varicella). Affected infants have a poor neurodevelopmental outlook.

Risk of neonatal VZV (severe, disseminated disease in newborn) if chickenpox is contracted by the mother 4 days before birth, to 2 days after  (risk 20%).  Before that, good chance that maternal immune response will protect baby, after that the dose of infection transmitted to the baby via the umbilical cord is likely to be small (although will still be exposed to droplets).

See Maternal for advice on varicella exposure in pregnancy and in neonates.