Heart rate patterns in normoxemic, hypoxemic, and anemic second-trimester fetuses

Fetal heart rate monitoring was performed immediately before cordocentesis on 71 occasions on 49 patients at 20 to 26 weeks' gestation. In the normoxemic, nonanemic fetuses, the basal fetal heart rate was 120 to 160 beats/minute, the baseline variability was more than 5 beats/min, and there were no prolonged decelerations. Accelerations were present in 19 of the 25 recordings. In the tracings from the hypoxemic (n = 11) or anemic (n = 35) fetuses, there was tachycardia, baseline variability of less than 5 beats/min, and prolonged fetal heart rate decelerations. However, the sensitivity of these pathologic patterns in predicting moderate-to-severe hypoxemia or anemia was 45% and 33%, respectively. The data demonstrate a gestation-dependent maturation of both normal and pathologic fetal heart rate patterns.