FETAL SPLENIC SIZE IN ANEMIA DUE TO RH-ALLOIMMUNIZATION

Objective: To determine whether fetal splenic enlargement predicts ane mia in Rh-alloimmunized nonhydropic singleton fetuses, Methods: Spleni c circumference was measured before funipuncture in 21 singleton pregn ancies an 47 occasions. The spleen was imaged in an axial section of t he fetal abdomen close to the level used for measurement of the abdomi nal circumference. The splenic length and width were measured and the circumference calculated by the formula (length and width x 1.57). One measurement per patient was used for each analysis. Splenic circumfer ence was measured and expressed as multiples of the normal median (MoM ) for gestational age. One hundred twenty-one cases were used to provi de cross-sectional normative data. The expected median splenic circumf erence Values were derived from a normal group. Fetal anemia was defin ed as hemoglobin deficit, ie, mean hemoglobin concentration for gestat ion minus the measured value, Anemia was defined as hemoglobin deficit exceeding 2 g/dL, and severe anemia as hemoglobin deficit exceeding 5 g/dL. Receiver operator characteristics curves for the prediction of anemia using different splenic circumference (MoM) values were constru cted. Results: Splenic circumference was an excellent predictor of sev ere anemia in cases with no prior transfusion: sensitivity 100% and sp ecificity 94.7% (area under the curve = .97, P < .03). The measurement did not correlate significantly with severe anemia in the group with prior transfusion (area under the curve = .73, P = .19). Conclusion: S plenomegaly is sensitive for the detection of severe anemia in nonhydr opic Rh sensitized cases without prior transfusion. The splenic enlarg ement could be explained by extramedullary erythropoiesis. (Obstet Gyn ecol 1998;92:828-32. (C) 1998 by The American College of Obstetricians and Gynecologists.).