Congenital varicella occurs when exposure happens during which period of pregnancy?

Congenital varicella syndrome is associated with maternal infection with the varicella virus during pregnancy, particularly when exposure occurs in the first 28 weeks. The risk of the fetus developing congenital varicella syndrome is highest when maternal varicella infection occurs in the first trimester, especially prior to 20 weeks of gestation.

However, it's important to note that exposure during the first 28 weeks of pregnancy is a critical window where significant risks are present, including the potential for the fetus to develop various abnormalities such as limb hypoplasia, cicatricial skin lesions, and ocular defects. This makes the period from conception to 28 weeks key in understanding the implications of maternal varicella infection.

As pregnancy progresses beyond 28 weeks, the risk for congenital varicella syndrome decreases significantly. While exposure during the third trimester can still lead to complications such as neonatal varicella infection at birth, the risk for congenital abnormalities is markedly less. Thus, recognizing the first 28 weeks as the period of concern provides clarity on why this timeframe is crucial for understanding the implications of varicella exposure in pregnancy.