ObjectiveTo determine the seronegativity rate of varicella-zoster virus in a tertiary care obstetric population.MethodsAt their initial prenatal visit, all obstetric patients at Westchester County Medical Center have a varicella-zoster virus IgG antibody titer (Varicella Stat; Biowhit-taker, Inc., Walkersville, MD) performed. A value of 0.99 or greater units is positive. Patients were divided into three groups: seronegative, seropositive, and those with no test results. Mean maternal age was compared among groups using the unpaired two-tailed Studentttest, withP< .05 considered significant.ResultsFrom February 1, 1994, to May 30, 1996, 927 women had an initial prenatal visit. Ninety-nine patients were varicella-zoster virus antibody negative (seronegativity 11.6%, which is significantly higher than that reported in other studies); 755 were varicella-zoster virus antibody positive, and 73 had no results. The mean age of the seronegative patients was 27 years and of the seropositive patients 28 years, which was not significantly different.ConclusionVaricella-zoster virus seronegativity is higher in our obstetric population than generally is reported in adults. This may reflect the number of immigrants from tropical countries attending metropolitan hospitals. Mathematic models evaluating the impact of varicella-zoster virus vaccination and decisions regarding screening and postpartum vaccination must be based on accurate epidemiologic data, particularly in view of the effect of varicella-zoster virus on pregnant women, their fetuses, and their neonates.