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Prenatal diagnosis of a transient myeloproliferative disorder in trisomy 21

We report the prenatal diagnosis of a transient myeloproliferative disorder suggestive of leukaemia in a fetus with hepatosplenomegaly, hydrops and 47, XY,+21 karyotype. The initial fetal white blood cell count at 26+5 weeks' gestation was 190/nl with 70 per cent blast cells. Immunophenotyping of the large blasts revealed surface markers suggestive of an early stem cell differentiation arrest resulting in undifferentiated polyclonal myelopoiesis. The fetal heart tracing showed minimal beat‐to‐beat variability in the presence of high leukocyte counts. Serial fetal blood sampling showed decreasing blast cells in the peripheral blood and normalization of white blood cell counts. Although there was increasing hydrops, this period was marked by improvement of the fetal heart rate pattern. Finally the fetus developed pancytopenia with increasing hydrops, AV‐valvular insufficiency and venous Doppler studies indicative of cardiac decompensation prior to intra‐uterine death at 31+5 weeks' gestation. Post‐mortem examination revealed marked liver and splenic necrosis without evidence of residual leukaemic infiltration in any organ.