Fetal heart rate patterns in red blood cell isoimmunized pregnancies.

Fetal heart rate was monitored in 33 red blood cell isoimmunized patients at 32 to 36 weeks' gestation immediately before cordocentesis. The fetal heart rate patterns were analyzed according to 25 different classifications, and the values were related to the fetal hemoglobin concentration, oxygen tension, and oxygen content. Nonreactive, suboptimal, or pathologic fetal heart rate patterns were encountered more commonly in fetuses that were hypoxemic and anemic than in those that were normoxemic and nonanemic. However, the positive predictive value of these abnormal fetal heart rate patterns with respect to fetal anemia was 50% to 100%; the negative predictive value was 18% to 40%.