The Varicella-Zoster Virus (VZV) causes chickenpox (the primary infection) and shingles (a reactivation of the virus later in life). Exposure to VZV during pregnancy requires immediate consultation with a healthcare provider. The risk level depends almost entirely on whether the pregnant woman is already immune to VZV. Understanding the nature of the exposure—shingles versus chickenpox—is the first step in assessing the potential risk to both the mother and the developing fetus.
Shingles Versus Chickenpox: Clarifying the Risk
Shingles represents the reawakening of VZV that has been dormant since a childhood chickenpox infection. Shingles lesions contain VZV, but the virus is not typically spread through the air or respiratory droplets like chickenpox. Transmission generally requires direct contact with the fluid from open blisters before they have crusted over.
A person exposed to shingles cannot contract shingles itself; instead, a non-immune person will develop chickenpox, the primary VZV infection. Since most adults are immune to VZV from prior infection or vaccination, the risk following shingles exposure is minimal for the majority of pregnant women. However, for non-immune women, exposure to a shingles rash poses a risk of developing chickenpox, which carries greater potential complications.
Evaluating Maternal Susceptibility and Fetal Consequences
Determining a pregnant woman’s immunity status is the first step following VZV exposure. Immunity is established through a documented history of chickenpox, two doses of the varicella vaccine, or a blood test detecting VZV IgG antibodies. If a non-immune woman contracts VZV, she will develop chickenpox, which carries risks for both her and the fetus.
Maternal complications from primary VZV infection include varicella pneumonia, the most frequent serious complication. This severe lung infection occurs in 10 to 20 percent of pregnant women who contract chickenpox, particularly later in gestation, and can be life-threatening. Other rare complications include encephalitis and hepatitis.
Fetal consequences depend heavily on the gestational age at which the mother develops chickenpox. Primary infection during the first and early second trimesters carries a slight risk (around 0.4% to 2%) of Congenital Varicella Syndrome (CVS). This rare condition is associated with birth defects:
- Limb hypoplasia
- Microcephaly
- Eye abnormalities
- Skin scarring
The highest risk period for CVS occurs between 13 and 20 weeks of gestation.
If the mother contracts chickenpox late in pregnancy, the risk of CVS is virtually zero, but the concern shifts to Neonatal Varicella. This severe infection occurs if the mother develops the rash between five days before delivery and two days after. During this critical window, the virus crosses the placenta before the mother can produce and pass protective antibodies to the newborn, resulting in a potentially fatal infection.
Immediate Post-Exposure Management and Treatment
Following significant VZV exposure when immunity is unknown or the mother is confirmed susceptible, an urgent blood test checks for VZV IgG antibodies. If immunity cannot be confirmed quickly, passive immunization is recommended.
This involves administering Varicella-Zoster Immune Globulin (VariZIG), a blood product containing VZV antibodies that provides immediate, temporary protection. VariZIG should be administered as soon as possible after exposure, ideally within 96 hours, though it may be effective up to 10 days post-exposure.
If the mother develops chickenpox, oral antiviral medication, such as acyclovir, is typically initiated within 24 hours of the rash onset to mitigate the severity and duration of the illness. For cases of severe maternal illness, such as varicella pneumonia, hospitalization and intravenous acyclovir are required.
Vaccine Guidance for Varicella-Zoster Virus
The varicella vaccine is a live-attenuated virus vaccine, meaning it contains a weakened form of the virus. For this reason, it is strictly contraindicated during pregnancy, and non-immune women must receive it before conception. Women who receive the varicella vaccine are generally advised to avoid becoming pregnant for one month after the final injection.
The Shingrix vaccine, which protects against shingles, is a non-live, recombinant vaccine. While safe for non-pregnant adults, it is not routinely recommended during pregnancy due to limited data. However, it poses no known risk if inadvertently administered.