What is chickenpox?

Chickenpox (varicella) is a very contagious disease. It happens most often in childhood. By adulthood, most people in the U.S. have had chickenpox or had the vaccine in childhood. More than 9 in 10 pregnant people are immune to chickenpox. But about 1 in 2,000 pregnant people in the U.S. will get chickenpox during pregnancy because they're not immune. Pregnant people who get chickenpox are at risk for serious health problems. 

The disease is caused by the varicella-zoster virus (VZV). This is a form of the herpes virus. It can be spread from person to person by contact with an infected person's rash. And it can spread through the air by a cough or sneeze. Chickenpox is contagious 1 to 2 days before the rash shows up until the blisters have dried and become scabs. Once a person is exposed to the virus, chickenpox may take up to 14 to 16 days to show up.

Risks of chickenpox in pregnancy

When a person has chickenpox in the first 20 weeks of pregnancy, there's a 1 in 50 chance for the baby to develop a set of birth defects. This is called the congenital varicella syndrome. It includes:

• Scars

• Defects of muscle and bone

• Malformed and paralyzed limbs

• Small head size

• Blindness

• Seizures

• Intellectual disability

This syndrome is rare if an infection occurs after 20 weeks of pregnancy.

Risks of chickenpox after birth

In a birth parent who gets the rash from 5 days before birth to 2 days after birth:

• Up to 3 in 10 newborns will be infected. They'll have a rash between 5 and 10 days after birth.

• Up to 3 in 10 of these babies will die if not treated.

If the birth parent has a rash between 6 and 21 days before birth:

• The baby has some risk of mild infection.

If the baby is treated right after birth with a shot of VZIG (varicella-zoster immune globulin):

• The infection can be prevented. Or it can make the infection less severe.

The chickenpox vaccine

In 1995, the FDA approved a chickenpox vaccine. If a pregnant person has had contact with someone who has chickenpox or shingles, VZIG can be given within 96 hours to prevent chickenpox, or lessen the severity. The severity of chickenpox in pregnancy may also be reduced by the antiviral medicine acyclovir. Pregnant people shouldn't have contact with anyone who has chickenpox if they aren't sure if they're immune.

The best way to protect against chickenpox is to get the chickenpox vaccine. People shouldn't get the vaccine during pregnancy or in the 30 days before trying to get pregnant, unless they've been exposed to chickenpox.