Parvovirus B19 Infection in Pregnancy

Fetal and Maternal Risks

The parvovirus B19 is the most common infectious cause of non-immune hydrops fetalis (NIHF), accounting for 5-10% of all cases, and has a predilection for fetal erythroid progenitor cells, causing inhibition of erythropoiesis and consequent fetal anemia 1, 2
The risk of fetal death is 15% between 13-20 weeks of gestation, and decreases to 6% after 20 weeks 1, 2
The risk of adverse fetal outcome is highest when congenital infection occurs in early second trimester (<20 weeks) 2

A diagnosis of past infection (at least 4-12 weeks prior) and protection against new infection is indicated by a positive IgG and negative IgM, requiring no intervention 3
Doppler of the middle cerebral artery (MCA-PSV) is the primary method for detecting fetal anemia 4

MCA-PSV evaluation should be reserved for patients at risk of having an anemic fetus 4
The correct technique involves assessing the middle cerebral artery near its origin, limiting overestimation of MCA-PSV, and using angle correction only if unavoidable 4
The threshold for intervention is an MCA-PSV >1.5 multiples of the median (MoM) or a hydropic fetus, at which point fetal blood sampling with preparation for intrauterine transfusion should be offered 4

Intrauterine transfusion (IUT) is indicated for fetuses at significant risk of severe fetal anemia (MCA-PSV >1.5 MoM or hydropic), with the goal of supporting the fetus through the aplastic crisis 4
The development of NIHF is associated with high mortality, and outcomes are significantly improved after intrauterine fetal transfusion 1, 2
IUT is recommended for NIHF due to parvovirus B19 infection, unless the pregnancy is at advanced gestational age and the risks associated with delivery are considered lower than those associated with the procedure 1, 2

Perinatal survival rates after IUT for parvovirus B19 range from 67% to 85% 4
These rates are lower than those for alloimmunization, likely due to the later diagnosis of severe fetal anemia in fetuses infected with parvovirus B19 presenting with hydrops 4

If a fetus is considered to be at significant risk of severe fetal anemia, the patient should be referred to a tertiary care center or a center with experience in invasive fetal therapy 4

Pregnancies with fetuses at risk of fetal anemia should be delivered at 37-38 weeks of gestation, unless indications for earlier delivery develop 4