A 24-year-old woman was gravida 1, para 0, with an early uneventful twin monochorionic diamniotic pregnancy and a tenth week ultrasound normally reported. In the thirteenth week of gestation the patient presented with fever for one week and pruritic vesicular eruptions on the skin, consistent with the classic presentation of chickenpox. The patient had no history of chickenpox in childhood and had not received immunization against it. No antiviral treatment was given. At 24 weeks of pregnancy the patient underwent a new ultrasound in which one of the fetuses presented with decreased head circumference and facial abnormalities.