Chickenpox and Pregnancy

Varicella zoster infection (commonly known as chickenpox) peaks in March, April and May, though it can be contracted any time of the year. Natural chickenpox infection usually occurs in early childhood; 90% of cases occur in individuals 10 years old or younger. In healthy children, serious complications are rare. But in adults, and especially in pregnant women, chickenpox can be fatal. With peak season upon us, it is important to review this disease.

Chickenpox typically presents with a fever, weakness and a skin rash. It is highly contagious; 95% of susceptible household contacts will develop the disease. The characteristic itchy "pox" begin on the trunk and then spread to the extremities. Patients are contagious from one day before the outbreak of the rash until all the skin lesions have dried and crusted over.

Pregnancy is "immunosuppressive," meaning it weakens the immune system. As a result, approximately 1% of pregnant women infected by the chickenpox virus will develop encephalitis, or a central nervous system infection. Encephalitis is frequently fatal and if not, can cause lifelong problems. Up to 20% of pregnant patients with chickenpox will develop a life-threatening pneumonia. All pregnant patients with chickenpox require hospitalization with intravenous antiviral treatment.

Congenital varicella results from chickenpox passage across the placenta to an unborn baby. This infection can cause the baby to die in the uterus. If the baby survives, multiple abnormalities (poorly formed limbs and muscles, small head, blindness, mental retardation) can result. Fortunately, even when the mother develops chickenpox at 13-20 weeks, her baby has only about a 1 in 50 chance of congenital varicella.

Although strong IV drugs can be used to treat the pregnant woman with chickenpox, a much better strategy is prevention. Women of reproductive age should be assessed for immunity to this infection, preferably before they become pregnant. Immunity to chickenpox is typically lifelong, so those with confirmed childhood infections can be reassured. Women without confirmed childhood infections can have blood testing for varicella antibodies; even among those with no recollection of prior infection, the vast majority will demonstrate antibodies, and thus, are immune.

A few women without prior infection will also demonstrate no antibodies and are thus non-immune. If already pregnant, these women MUST avoid contact with chickenpox. Additionally, it is critical to avoid herpes zoster (or "shingles"), as this can also be infectious to individuals who are not immune to chickenpox. If not pregnant, Varivax (the chickenpox vaccine) can be administered. Varivax, given to adults as two doses 4-8 weeks apart, is 70-80% effective in protecting the patient from chickenpox. Women should avoid pregnancy for three months after vaccination. If already pregnant, and a documented exposure has occurred to a nonimmune woman, varicella zoster immune globulin (VZIG) can be given. VZIG is 60-80% effective in preventing infection, but ONLY if given in the first 72-96 hours after initial exposure.

In conclusion, chickenpox can be very harmful to pregnant women and their babies. The best strategy is prevention, preferably by vaccinating susceptible women before they become pregnant. Women should discuss their chickenpox immunity status with their doctor before planning a pregnancy.

By Scott G. Williams, MD, FACOG, of SSM St. Charles Clinic Medical Group, O’Fallon, MO.