Ans. is 'b' i.e., Crosses placenta in only < 10% of cases (Ref: Jawetz, 24th/e, p. 414, 417)* Maternal infection with B19 virus may pose a serious risk to the fetus, resulting in hydrops fetalis and fetal death due to severe anemia. Fetal loss occurs in fewer than 10% of primary maternal infections and death occurs most commonly before the 20th week of pregnancy. Although there is frequent intrauterine transmission of human parvovirus (with estimates of vertical transmission rates of 30% or higher).