Greatest fetal risk from intrauterine varicella infection occurs when exposure is during which gestational window?

• A. 13-20 weeks
• B. 0-12 weeks
• C. 21-28 weeks
• D. After 28 weeks

Answer: (A)

Varicella infection during pregnancy affects the fetus differently depending on when the mother is infected. The period when the fetus is most vulnerable to congenital varicella syndrome is mid-gestation, roughly the second trimester between about 13 and 20 weeks. During this time, organ development for skin, limbs, eyes, and the central nervous system is actively occurring, so viral invasion can disrupt these processes and lead to the characteristic congenital varicella syndrome features such as dermal scarring in a dermatomal pattern, limb hypoplasia, and CNS or ocular abnormalities.

In the first trimester, infection can increase the risk of miscarriage or more general fetal abnormalities, but the classic congenital varicella syndrome is most strongly linked to the mid-second-trimester window. After about 28 weeks, the concern shifts more toward neonatal varicella if the mother becomes infected near delivery, because the fetus may not have sufficient time to develop protective maternal antibodies.

So the window with the greatest fetal risk for congenital varicella syndrome is during 13–20 weeks of gestation.