Parvovirus B19 (B19V) Infection and Pregnancy

Human parvovirus B19 (B19V; genus Erythrovirus) is a small, non-enveloped, single-stranded DNA virus which causes the common childhood exanthem fifth disease, or 'slapped-cheek syndrome'. Infection during pregnancy can cause severe fetal anaemia and nonimmune hydrops fetalis (NIHF), often leading to miscarriage or fetal death. B19V has a pronounced tropism for rapidly proliferating erythroid progenitor cells (EPC) leading to the cessation of erythropoiesis. The fetus is particularly vulnerable to adverse outcome following B19V infection due to rapid fetal blood volume expansion and a reduced reticulocyte half-life. B19V is not a significant teratogen. The risk to the fetus is increased if maternal infection occurs during the first two trimesters. Approximately 35-45% of women of child bearing age are not immune to B19V. Maternal seroconversion during a seasonal epidemic may reach 10%. Vertical transmission following infection is estimated at 33%, therefore a significant proportion of pregnancies are vulnerable to fetal infection. However, approximately 50% of primary infections are asymptomatic and may go undetected until adverse fetal outcome becomes apparent. This could be reduced if B19V awareness amongst pregnant women was heightened. Prenatal screening of antenatal booking-bloods would identify at-risk pregnancies and appropriate advice could be given to mothers at this stage. Recommended case management following maternal primary B19V infection is regular Doppler ultrasound monitoring of the middle cerebral artery peak systolic flow velocity for a 12 week follow-up period. Treatment of severe fetal anaemia is cordocentesis transfusion with a success rate of approximately 80%.