Parvovirus B19 Infection in Pregnancy: Maternal and Fetal Viral Load Measurements Related to Clinical Parameters

Parvovirus B19 (B19V) is a DNA virus of worldwide distribution that causes erythema infectiosum (fifth disease). Approximately 35% to 45% of women of reproductive age lack protective immunoglobulin G (IgG) antibody against B19V. Infection rates may reach 10% or higher during endemic periods. When infection occurs during pregnancy, vertical transmission from mother to fetus occurs in one-third to one-half of cases, and in 10% there is an adverse fetal outcome such as myocarditis, anemia, endothelial injury, or cerebral damage. This prospective study of 20 cases related clinical findings to both the quantitative B19V viral load and values of IgG and IgM in maternal and fetal blood samples acquired during intrauterine erythrocyte transfusion (IUT) for B19V-induced fetal anemia. The fetal viral load was estimated using the quantitative real-time polymerase chain reaction technique, and antibody levels by enzyme immunoassay. Fourteen of the 20 infants, 70% of the total, survived. Two markedly hydropic fetuses died in cardiac arrest during IUT, possibly because of volume overload. Four other fetuses died in utero following IUT. Two surviving fetuses delivered preterm, but there were no small-for-gestational age infants. Maternal levels of IgG and IgM antibodies exceeded fetal levels. The fetal B19V viral load correlated significantly with the maternal viral load (r = 0.856; P = 007), but exceeded the maternal load 10 5 -fold (P < 0001). The maternal titer of B19V IgM correlated positively with the fetal load. There was, however, no apparent relationship between the fetal viral load and the severity of fetal anemia as determined by Doppler flow measurements in the middle cerebral artery. The major finding in this study is the consistent presence of an extremely heavy viral load in B19V-infected fetuses. In addition, the fetal and maternal viral loads correlated significantly. It appears possible to reliably estimate the viral load in fetal blood samples taken during sessions of IUT. Possibly the finding of a positive relationship between the fetal and maternal viral loads reflects ongoing maternal infection, but it is more likely that the fetus is a source of persistent viremia in the maternal circulation. With more data, maternal IgM titers and viral load values might be used to predict the severity of fetal B19V infection.