Varicella and Pregnancy

What is varicella?

Varicella (or chickenpox) is a highly infectious disease, usually associated with childhood. By adulthood, the vast majority of Americans have had chickenpox or have previously been vaccinated in childhood. Although more than 90% of pregnant women are immune to chickenpox, about 1 in 2,000 pregnant women in the United States will develop chickenpox during pregnancy because they are not immune. Pregnant women who get chickenpox are at risk for serious complications. 

The disease is caused by the varicella-zoster virus (VZV). This is a form of the herpes virus. Transmission happens from person-to-person by direct contact with an infected person's rash, or through the air by a cough or sneeze. Chickenpox is contagious one to two days before the appearance of the rash until the blisters have dried and become scabs. Once exposed to the virus, chickenpox may take up to 14 to 16 days to develop.

When a woman has a varicella infection during the first 20 weeks of pregnancy, there is a 2% chance for the baby to develop a group of birth defects called the "congenital varicella syndrome." This includes scars, defects of muscle and bone, malformed and paralyzed limbs, a small head size, blindness, seizures, and intellectual disability. This syndrome rarely happens if the infection happens after 20 weeks of pregnancy.

Another time there is a concern with a varicella infection is during the newborn period, if the mother develops the rash from 5 days before to 2 days after delivery. Up to 30% of newborns will be infected in this case. They will develop a rash between 5 and 10 days after birth. Up to 30% of infected babies will die if not treated. If the mother develops a rash between 6 and 21 days before delivery, the baby faces some risk of mild infection.

If the baby is treated immediately after birth with an injection of VZIG (varicella-zoster immune globulin), the infection can be prevented or the severity lessened.

In 1995, the FDA approved a chickenpox vaccine. If a pregnant woman has been exposed to someone with chickenpox or shingles, VZIG can be given within 96 hours to prevent chickenpox, or lessen the severity. It is important for pregnant women to avoid exposure to anyone with chickenpox if they are not sure whether they are immune to this infection.

The best way to protect against chickenpox is to get the chickenpox vaccine. Women should not get vaccinated during pregnancy or during the 30 days before becoming pregnant.