Is it risky to be exposed to chicken pox during pregnancy?
It depends. If you've had chicken pox before, you're probably immune, so there's little cause for worry. Up to 95 percent of adults in the United States are immune, including many people who had chicken pox and never even knew it. If you received the chicken pox vaccine (available in the United States since 1995), you're also probably immune.
A single dose of the chicken pox vaccine, which was the standard dose when it was first offered, prevents chicken pox altogether for about 80 to 85 percent of those who were vaccinated and prevents a severe case for most of the rest. Since then, research has shown that a second dose provides more protection, so the Centers for Disease Control and Prevention (CDC) now recommends getting two doses of the chicken pox vaccine.
Since so many adults are immune, not many pregnant women get chicken pox – estimates range from 1 to 7 cases for every 10,000 pregnancies. But if you're not immune and you do happen to catch the disease while you're pregnant, you could get quite sick, and there's a small chance that it would affect your baby. If you're not sure whether you're immune, a simple blood test can give you the answer.
What would happen to my baby if I got chicken pox while I'm pregnant?
Chances are good that no harm would come to your baby, but timing is a factor. If you get chicken pox during the first or second trimester of pregnancy, there's a slight risk (probably less than 2 percent overall) that your baby will get something called congenital varicella syndrome (CVS). The risk is highest if you're infected between 13 and 20 weeks' gestation.
CVS is characterized by birth defects, most commonly skin scarring, malformed limbs, an abnormally small head, neurologic problems (like intellectual disability), and vision problems. Plus, a baby with CVS may also grow poorly in utero and suffer from seizures and physical and mental developmental disabilities. The infection may also increase the risk of miscarriage or later fetal death.
If you do contract chicken pox, you'll have a detailed ultraound to look for signs of defects or other problems and at least one follow-up sonogram to see how your baby is doing later on. You may also choose to meet with a genetic counselor to discuss the risks in your particular case and decide how you want to proceed.
Is my baby at risk if I get chicken pox close to my due date?
If you get chicken pox early in the third trimester of pregnancy, your baby will probably be fine. Here's why: About five days after you come down with chicken pox, your body develops antibodies to the virus and passes them to your baby through the placenta, offering protection that his own immature immune system couldn't provide on its own.
If you develop chicken pox five to 21 days before your baby is born, he might develop chicken pox, but because of the antibodies he received from you, it's much less likely to be serious. (Some babies exposed to chicken pox in utero don't have any signs of infection at birth but develop a case of shingles during infancy or early childhood without having had chicken pox. Fortunately, it's usually not serious.)
The most risky time to come down with chicken pox is between five days before giving birth and two days after delivery, because then your baby is exposed to the virus but doesn't have time to receive antibodies from you. In this case, there's a high chance (estimated at 17 to 30 percent) that he'll develop what's called neonatal varicella, or newborn chicken pox, which can be serious and even life threatening – especially if left untreated.
Fortunately, your baby's risk of a severe case can be greatly reduced if he gets a shot of varicella zoster immune globulin (VZIG), a blood product that contains chicken pox antibodies. (You may also see this referred to as VariZIG, which is the brand name of the VZIG product that's currently available in the United States.) Your baby will be given the shot soon after birth if your chicken pox showed up within five days of delivery or as soon as you discover your rash if it's within two days after delivery.
If your newborn shows any sign of developing the infection – such as coming down with a fever or showing a rash of even a few spots – he'll be treated intravenously with the antiviral drug acyclovir.