Chicken pox is usually a benign, self-limited, viral infection caused by the varicella virus. However, chicken pox acquired during pregnancy causes an increase risk of complications to the mother and the infant. The time of infection, during early pregnancy or near delivery, determines the risk to mother and child.
Pregnant Women Exposed to Chicken Pox
Pregnant women who have a history of a previous chicken pox infection or who have been immunized have antibodies to the virus. These antibodies are transferred to the infant through the placenta throughout the pregnancy. Therefore, pregnant women who are immune and are exposed to someone with chicken pox do not need to worry about complications for themselves or their infant.
Testing for Immunity in Pregnancy
All women should be questioned about previous chicken pox infection or immunization at their first prenatal visit. Of those women who do not remember a past infection or immunization, 80% to 90% have antibodies and are considered immune. For this reason, testing for antibodies is controversial, but many practitioners obtain this test at the first prenatal visit.
Maternal Complications of Chicken Pox in Pregnancy
A primary chicken pox infection occurs in only 0.05% to 0.07% of pregnancies because most women of childbearing age have immunity to the varicella virus because of a previous infection or immunization. Women who do acquire chicken pox while pregnant, especially in the third trimester, are at a greater risk of developing varicella pneumonia. Varicella pneumonia is a potentially life-threatening infection of the lungs by the varicella virus.
Infant Complications of Chicken Pox in Early Pregnancy
Primary chicken pox infection in the first trimester of pregnancy, especially weeks 8 to 12, carries a 2.2% risk of congenital varicella syndrome, a syndrome of birth defects in the infant. The most common manifestation of congenital varicella syndrome is scarring of the skin. Other abnormalities that can occur include a smaller than normal head, eye problems, low birth weight, small limbs, and mental retardation.
Infant Complications of Chicken Pox in Late Pregnancy
If a woman acquires a primary chicken pox infection within 5 days before and 2 days after delivery, her newborn is at risk for disseminated varicella infection. Disseminated varicella infection occurs when the virus infects a newborn before the transfer of protective maternal antibodies. This overwhelming viral infection leads to death in 25% of cases.
Treatment of Pregnant Women with Chicken Pox
Women who acquire primary chicken pox during pregnancy should be treated with the antiviral drug acyclovir (Zovirax) which seems to be safe in pregnancy. Pregnant women with varicella pneumonia should be treated with IV acyclovir and be observed in the hospital. In addition women who are not immune to varicella, but are exposed may be treated with varicella-zoster immunoglobulin (VZIG), a substance that triggers an immune response against the varicella virus.
Treatment of Infants with Chicken Pox
Infants whose mothers develop varicella 5 days before delivery or 2 days following delivery should receive VZIG after birth. Infants who develop varicella during the first 2 weeks of life should be treated with IV acyclovir.