Relationship of systolic/diastolic ratios from umbilical velocimetry to fetal heart rate

We assessed the relationship between systolic/diastolic ratios as determined by umbilical velocimetry to fetal heart rate. Umbilical velocimetry was performed with continuous-wave Doppler ultrasound and systolic/diastolic ratios and fetal heart rate for the corresponding cardiac cycles were calculated in four groups of patients. Group 1 consisted of 30 patients undergoing antepartum fetal testing; systolic/diastolic ratios were found to be significantly lower (mean +/- SD, 2.0 +/- 0.15) during an evoked fetal heart rate acceleration with an artificial larynx than either before (2.4 +/- 0.14) or after the acceleration (2.35 +/- 0.10, p less than 0.01). In 20 patients with pyelonephritis (group 2), systolic/diastolic ratios were significantly lower during initial fetal tachycardia (1.6 +/- 0.21) as compared with those obtained after its resolution (2.1 +/- 0.12, p less than 0.08). In the 25 patients with chorioamnionitis in group 3, systolic/diastolic ratios were significantly higher during initial fetal tachycardia (1.4 +/- 0.21) than after its resolution (1.9 +/- 0.15, p less than 0.05). Twenty patients in labor (group 4) had 10 serial measurements at 1 to 2-hour intervals of systolic/diastolic ratio and FHR. Least-squares regression of each patient showed a negative slope that differed statistically from zero (p less than 0.05). There were no patients with elevated systolic/diastolic ratios greater than 3.0 in any group and all patients delivered fetuses appropriate for gestational age. These findings suggest an inverse relationship between systolic/diastolic ratio and fetal heart rate. Additionally, an alteration in fetal heart rate within the range studied does not itself produce abnormal ratios. Therefore normalization of the systolic/diastolic ratio for heart rate may be considered in clinical studies for statistical analysis and comparison but may have little practical or clinical relevance when the ratios are abnormal.