Fetal thrombocytopenia in pregnancies with fetal human parvovirus-B19 infection

Fetal infection with human parvovirus B19 (hParvo-B19) has been associated mainly with fetal anemia, although data regarding other fetal hematologic effects are limited. Our aim was to assess the rate and consequences of severe fetal thrombocytopenia after fetal hParvo-B19 infection.

We conducted a retrospective study of pregnancies that were complicated by fetal hParvo-B19 infection that underwent fetal blood sampling (FBS). The characteristics and outcomes of fetuses with severe thrombocytopenia (<50 × 10(9)/L) were compared with those of fetuses with a platelet concentration of ≥50 × 10(9)/L (control fetuses). Fetuses in whom 3 FBSs were performed (n = 4) were analyzed to assess the natural history of platelet levels after fetal hParvo-B19 infection.

A total of 37 pregnancies that were affected by fetal hParvo-B19 infection were identified. Of the 29 cases that underwent FBS and had information regarding fetal platelets, 11 cases (38%) were complicated by severe fetal thrombocytopenia. Severely thrombocytopenic fetuses were characterized by a lower hemoglobin concentration (2.6 ± 0.9 g/dL vs 5.5 ± 3.6 g/dL; P = .01), lower reticulocyte count (9.1% ± 2.8% vs 17.3% ± 10.6%; P = .02), and lower gestational age at the time of diagnosis (21.4 ± 3.1 wk vs 23.6 ± 2.2 wk; P = .03). Both the fetal death rate within 48 hours of FBS (27.3% vs 0%; P = .02) and the risk of prematurity (100.0% vs 13.3%; P < .001) were higher in fetuses with severe thrombocytopenia. Fetal thrombocytopenia was more common during the second trimester but, in some cases, persisted into the third trimester. Intrauterine transfusion (IUT) of red blood cells resulted in a further mean decrease of 40.1% ± 31.0% in fetal platelet concentration.

Severe fetal thrombocytopenia is relatively common after fetal hParvo-B19 infection, can be further worsened by IUT, and may be associated with an increased risk of procedure-related fetal loss after either FBS or IUT.