Unexpected Cardiotocographic Deterioration in Fetal Transient Abnormal Myelopoiesis

Fetal transient abnormal myelopoiesis (TAM) can rarely occur without prenatal ultrasonographic abnormalities. We describe a case in which fetal compromise was first detected by cardiotocography (CTG). A previously uncomplicated pregnancy showed normal fetal growth and no structural abnormalities on serial ultrasonography. At 38+1 weeks of gestation, CTG revealed markedly reduced baseline variability with recurrent late decelerations, prompting emergency cesarean delivery. The male neonate, who had features of trisomy 21, exhibited marked leukocytosis with circulating blasts. Placental examination revealed intravascular blasts within both chorionic villous and umbilical cord vessels, confirming fetal TAM. Although peripheral blasts initially regressed, acute megakaryoblastic leukemia developed during infancy and required chemotherapy. Fetal TAM may occur without characteristic prenatal sonographic findings, and sudden CTG deterioration may be the first sign of fetal compromise. Placental and umbilical cord pathology can provide crucial postnatal evidence of in utero hematologic disease.