Fetal Anaemia Due to Parvovirus

Fetal anaemia due to parvovirus is suppression of fetal red cell production by parvovirus B19 infection of erythroid precursors, with severe anaemia, heart failure and hydrops. Maternal infection can cause fetal infection, and untreated hydrops can end in fetal death. It matters because the risk window is 4 to 12 weeks after maternal infection and intrauterine transfusion corrects the anaemia.

• Risk factors: contact with children with fever and rash, nursery or school staff, sickle cell disease or other haemolytic anaemia in the mother.
• Highest risk before 20 weeks.
• Most infected fetuses recover without treatment.

Women have a flu-like illness, rash on the cheeks and trunk, arthralgia, or no symptoms. Fetal anaemia causes reduced movements, polyhydramnios and hydrops.

• Rash (slapped cheek) in some.
• Large uterus for dates with ascites in hydrops.
• Differential diagnosis: rubella, measles, cytomegalovirus, red cell alloimmunisation, alpha thalassaemia, fetomaternal haemorrhage, other causes of hydrops, malaria.
• Complications: hydrops fetalis, stillbirth, myocarditis, thrombocytopenia, neonatal anaemia, aplastic crisis in mothers with sickle cell disease.

The approach is serology with weekly Doppler assessment of the fetal middle cerebral artery.

• Maternal parvovirus B19 IgM and IgG; IgM positive with IgG negative or low suggests acute infection; PCR on maternal blood or amniotic fluid.
• Middle cerebral artery peak systolic velocity weekly for 8 to 12 weeks after infection (above 1.5 multiples of the median means moderate to severe anaemia).
• Ultrasound for hydrops: ascites, pleural effusion, pericardial effusion, skin oedema, placental thickening, cardiomegaly, polyhydramnios.
• Fetal blood sampling for haemoglobin, platelets and reticulocytes at transfusion where available; maternal full blood count.

The principle is surveillance with Doppler and intrauterine transfusion for anaemia, as there is no antiviral drug.

• Supportive: avoid contact with infected people; hand hygiene; maternal rest and fluids; counselling about the risk of hydrops; plan care in a fetal medicine unit.
• Pharmacological: paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours) for fever and arthralgia; betamethasone 12 mg IM twice, 24 hours apart, before transfusion at 24 to 34 weeks and 6 days; no antiviral exists; for immunosuppressed women with chronic infection give immunoglobulin 0.4 g/kg IV daily for 5 days.
• Procedures: intrauterine transfusion with O negative, cytomegalovirus negative, irradiated packed cells (haematocrit 75 to 80 percent) through the umbilical vein for peak systolic velocity above 1.5 multiples of the median or hydrops, to a target fetal haematocrit of 40 to 50 percent, repeated if anaemia returns (usually one or two transfusions are enough); delivery at term, earlier only for failed treatment or fetal compromise.
• Special groups: women with sickle cell disease or other haemolytic anaemia may develop aplastic crisis and need urgent haemoglobin and transfusion (packed cells 1 unit over 3 to 4 hours); healthcare and school staff with exposure have serology within 3 weeks of contact.
• Red flags: hydrops, peak systolic velocity above 1.5 multiples of the median, reduced fetal movements, new polyhydramnios, bradycardia.
• Follow-up: Doppler weekly for 8 to 12 weeks; repeat scan 1 week after transfusion; growth scans every 4 weeks; newborn blood count and platelets; paediatric review.