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What is varicella?

Varicella (or chickenpox) is a highly infectious disease, usually associated with childhood. By adulthood, more than 95 percent of Americans have had chickenpox. Eighty-five to ninety-five percent of pregnant women are immune to chickenpox, which means that there is no need to be concerned about this during pregnancy, even if the woman is exposed to someone with chickenpox. Nearly seven women out of 10,000 will develop chickenpox during pregnancy, however, because they are not immune.

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, or through the air. 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 18 days to develop.

When a woman has a varicella infection during pregnancy, if during the first 20 weeks, there is a 2 percent chance for the baby to have a group of defects called the "congenital varicella syndrome," which includes scars, defects of muscle and bone, malformed and paralyzed limbs, a small head size, blindness, seizures, and mental retardation. This syndrome is rarely seen if the infection occurs after 20 weeks of pregnancy.

Another time that there is a concern with a varicella infection is in the newborn period, if the mother develops the rash from five days before, to two days after delivery. Between 25 percent 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 US Food and Drug Administration (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 if they are not sure whether they are immune to this infection.

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