Fetal parvovirus B19 infection

Fetal parvovirus B19 infection is a type of in utero infection. In certain cases it can lead to intrauterine fetal death. 

Pathology 

It was first reported to be associated with fetal death and hydrops fetalis in 1984. Human parvovirus B19 is the only known parvovirus virus pathogenic to humans. It is a small single-stranded DNA virus and a potent inhibitor of erythropoiesis, due to its cytotoxicity to erythroid progenitor cells ⁸. The virus is able to cross the placenta of women infected during pregnancy. Parvovirus B19 may be transmitted from mother to fetus transplacentally in ~30% of maternal infections.

Amongst its many other features, it is notorious for causing profound fetal anemia mainly as a result of the parvovirus avidly attacking fetal red blood cells. 

The fetus affected by B19 essentially resembles adults and children with chronic hemolytic anemias due to decreased erythrocyte production. High-output cardiac failure, secondary to anemia, leads to fluid accumulation and hydrops fetalis. Myocarditis leading to heart failure may also contribute to the development of fetal hydrops.

The risk of maternal to fetal transmission is higher in the 1^st and 2^nd trimesters. Approximately one-quarter of the women infected during pregnancy may transmit the virus to the fetus.  

Markers

• maternal B19-specific IgG: indicates past infection/immunity

• maternal B19-specific IgM: indicates recent infection

Radiographic features

Antenatal ultrasound

There can be some overlap in sonographic features which are also common to other fetal infections. Sonographically-detectable features include:

• presence of fetal ascites

• development of generalized hydrops fetalis 

• fetal hepatomegaly

• placentomegaly

• polyhydramnios

• increased (>95^th centile) cardiac biventricular outer diameter

Doppler ultrasound

The presence of fetal anemia can lead to changes in the fetal MCA Doppler flow from high to low resistance.

Treatment and prognosis

A significant part of management is focused on treating the fetal anemia, in appropriate cases, cordocentesis followed by intrauterine transfusion with packed red cells into the umbilical vein can be performed. The development of hydrops fetalis indicates a poorer prognosis.

Complications

• hydrops fetalis (from fetal anemia and/or involvement of cardiac myocytes): parvovirus infection can cause up to 27% of cases of non-immune hydrops fetalis ¹⁰

Differential diagnosis

For sonographic features consider: 

• other causes of intrauterine infection

• other causes of hydrops fetalis

• other causes of fetal anemia