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 percent of pregnant women are immune to chickenpox, about 1 in 2,000 pregnant women in the United States will develop chickenpox during pregnancy, however, 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), which is a form of the herpes virus. Transmission occurs 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 percent 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 mental retardation. This syndrome rarely occurs 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 five days before to two days after delivery. Between 25 and 50 percent of newborns will be infected in this case, and develop a rash between five and 10 days after birth. Up to 30 percent of infected babies will die if not treated. If the mother develops a rash between six and 21 days before delivery, the baby faces some risk of mild infection.
In 1995, the FDA approved a chickenpox vaccine. 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.
If a pregnant woman has been exposed to someone with chickenpox, 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 or shingles 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.
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