If a woman who is pregnant and nonimmune becomes infected by B19V [B19], infection of the fetus may occur. Of pregnant women with B19V infection, transplacental infection occurs in approximately 33% of cases. Because fetal RBCs have a shorter half-life of 45-60 days (vs 90 d in normal erythrocytes) infection may cause severe anemia in the fetus. The fetus may develop signs of high output cardiac failure (hydrops fetalis).