Chicken pox: Will my baby be affected?

What are the effects of contracting chicken pox on the fetus at around 18 weeks of pregnancy?

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Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

The answer to your question is a little difficult to answer because there have not been a lot of good studies on this subject. This is due to the fact that most girls acquire chicken pox before they reach child bearing age thus being immune when they become pregnant.

The effects of chicken pox on the fetus are known. Most commonly, the fetus has no discernable effects from the maternal infection. Those that are affected, most commonly have limb defects. Others may have a rash that utimately leads to scarring or acquire a skin infection called zoster. Other problems including brain defects have been reported but are considered uncommon.

What is unknown is what, if any, effect the "timing of the infection" in pregnancy has on the chances the fetus may be affected. However, there has been one recent study on the subject that may provide some insight.

What was found is that all cases of congenital varicella (chicken pox infection in the fetus caused by the pregnant mother getting chicken pox) occurred when the mother acquired chicken pox before the 20th week of pregnancy. The highest risk (2%) occurred in those that became infected during the 13-20th week. Of those babies that were affected, most had arm or leg malformations, skin lesions, and one died of complications due to the infection.

Nicole, this is only one study, but it is the best information we have thus far at estimating the chances of having fetal effects due to the mother's infection. It is important to note that the chances of an 18 week fetus having problems due to the infection are probably no greater than 2%.

However, I also realize that this is probably no comfort to a mother concerned about her baby. Careful follow up with the obstetrician doing ultrasounds will help in seeing if there are any problems due to the infection.

One last thing to note: If a pregnant woman who has never had chicken pox comes in contact with someone who currently has the infection, her obstetrician should be notified immediately. There is evidence that treatment of the mother with a drug called varicella zoster immune globulin decreases the severity of the disease and may substantially decrease the chances of the infant being affected. Unfortunately, most people do not realize when they have been exposed to the chicken pox virus.

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