Fetal Hydrops Secondary to in utero Pancytopenia.

Nonimmune hydrops remains a challenge in the prenatal setting with many cases not having a clear etiology determined prior to birth. We present an unusual case of one fetus of a dichorionic twin pair presenting at 24 weeks' gestation with hydrops and fetal pancytopenia with complete absence of white cells of unknown etiology, as revealed by cordocentesis. Serial red blood cell transfusions resulted in resolution of hydrops and continuation of the pregnancy until 35 weeks' gestation. Pancytopenia was noted throughout gestation and persisted in the newborn period. Moreover, the T-cell receptor excision circle (TREC) assay, a newborn screening test for severe T-cell deficiency, was abnormal at birth. Further evaluation revealed detectable TRECs and normal response to lymphocyte mitogens indicating some preserved thymic and lymphocyte function. The affected child had spontaneous resolution of the pancytopenia, including her severe T-cell deficiency, by 10 weeks of life. There has been no recurrence as of 24 months of age. The self-resolving nature of the pancytopenia is an important feature of this case of nonimmune hydrops. The abnormal TREC assay at birth in the affected infant may help explain the discordant prenatal findings.