Chickenpox can have teratogenic effects on a fetus. If a pregnant person develops chickenpox in the first 20 weeks of pregnancy, there is a slight risk of a rare, but serious, birth defect known as congenital varicella syndrome. A fetus with congenital varicella syndrome is at risk of developing skin scars, abnormalities of the eyes, legs, arms, and brain, as well as gastrointestinal problems. If a pregnant person develops chickenpox around the time of delivery, the newborn may be at risk of a life-threatening condition called neonatal varicella, which can result in severe or fatal illness of the newborn within a few days of delivery.