Management of fetal hemolytic disease by cordocentesis. I. Prediction of fetal anemia.

Between January 1985 and November 1990, 128 pregnancies complicated by maternal red blood cell alloimmunization were referred to our Fetal Diagnosis and Treatment Unit. We examined the premise that an evaluation of fetal blood would accurately identify fetuses at risk of requiring antenatal transfusion therapy. Two hundred seventy-two diagnostic cordocenteses were performed. Criteria for the timing of repeat cordocenteses were developed retrospectively on the basis of the fetal hematocrit values, reticulocyte counts, and direct Coombs' test results of the first 84 pregnancies. These criteria were tested and confirmed prospectively on the next 44 pregnancies. On the basis of the first blood sample, four hematologic patterns (and their distributions) were identified in the 98 antigen-positive fetuses. Pattern 1: fetuses at low risk of having significant antenatal anemia (hematocrit less than 30%) (n = 11, 11%). These fetuses had normal hematocrit values and reticulocyte counts coupled with negative or trace-positive direct Coombs' test. No fetus in this group had significant antenatal anemia. Pattern 2: fetuses at intermediate risk of having anemia (n = 29, 31%). Pattern 2 fetuses had normal hematocrit values and either direct Coombs' titers of more than trace less than or equal to 2+ and normal reticulocyte counts or low reticulocyte counts (less than 2.5th percentile for gestation). Twenty-one percent (n = 6) of fetuses in pattern 2 had significant antenatal anemia. Patterns 3 and 4: fetuses at greatest risk of having severe anemia. These fetuses had normal hematocrit values associated with either reticulocyte counts greater than 97.5th percentile for gestation or a direct Coombs' test greater than or equal to 3+ (pattern 3, n = 49, 50%) or both, or a mild anemia (greater than 30% but less than 2.5th percentile for gestation) (pattern 4, n = 9, 10%). Eighty percent (n = 39) of fetuses with pattern 3 and 90% (n = 8) with pattern 4 developed a hematocrit value less than 30%. We conclude that evaluation of fetal hemolytic disease with a fetal blood specimen permits the identification of fetuses at high risk of having antenatal anemia.