In the United States, chickenpox is an uncommon infection during pregnancy. Because VZV is not a reportable disease in most parts of the United States, the exact incidence is difficult to know. Large prospective studies completed decades ago calculated the incidence of maternal VZV during pregnancy as 0.8 in 10,000. A more recent study predicted an incidence rate as high as 7 in 10,000. Physicians caring for immigrants from tropical countries may see a higher incidence of disease, because chickenpox is not a universal infection of childhood in countries outside temperate climate zones. Although pregnant women with chickenpox may develop pneumonia and premature labor, a more recent prospective study of approximately 1,400 pregnant European women with chickenpox found no maternal deaths.

Transplacental VZV infection may occur in as many as 25% of infants whose mothers develop chickenpox during pregnancy. However, very few neonates develop symptomatic congenital infection. Transplacental infection with subsequent clinical sequelae in the fetus has been well described but is very uncommon and dependent on the timing of the infection. In a cohort of women followed prospectively in the United States, the frequency of congenital VZV syndrome was 0.4%. Based on other studies, the incidence rate of embryopathy associated with maternal infection is 2.2% and linked with infection during the first 20 weeks of gestation.

A neonate can acquire VZV infection in utero from a mother who is in the viremic stage of chickenpox or postnatally from exposure to infectious respiratory secretions or vesicular fluid in a patient with chickenpox or zoster. After inoculation of the virus onto the surface of the upper respiratory tract or the conjunctivae, the virus replicates locally, before disseminating in 4 to 6 days via an asymptomatic primary viremia. After replication in the liver, spleen, and possibly other sites for another 6 to 8 days, the virus disseminates widely in a high-grade viremia that may be accompanied by typical prodromal signs such as fever, malaise, and anorexia. The characteristic lesions of VZV are vesicles that develop in another 1 to 2 days. Vesicles on the skin are thin walled and filled with a clear fluid, often described as “dewdrops on a rose petal.” In chickenpox, the vesicles evolve over several days from macule, to papule,
vesicle, pustule, and crusted lesion and occur in various stages on any mucocutaneous surface. The incubation period for the development of disease is 10 to 21 days, with an average appearance of the rash at 14 days. Patients are infectious for 1 to 2 days before the development of a rash and for 5 days after the last vesicle has crusted. The virus is highly infectious, with attack rates of up to 90% reported in household settings.