Critical comparison of indices and threshold values for assessing placenta performance using Doppler ultrasound.

ABSTRACT

To determine the most appropriate index and an optimal cutoff value for obstetric Doppler ultrasound, the umbilical and uterine arteries of 467 patients were examined during the third trimester using an Acuson 128 color Doppler system. Doppler ultrasound detection of chronic placental insufficiency with fetal growth retardation and acute placental insufficiency with subpartal asphyxia were selected as criteria. A birth weight below the 10th percentile (using Hohenauer's percentiles) was taken as the parameter for the former and a 5-minute Apgar score of < 8 for the latter criterion. For each artery, two risk groups were studied 103 patients with chronic and 27 patients with acute placental insufficiency. Using EROC curves, the prediction of chronic and acute placental insufficiency was computed for six Doppler indices (maximum systolic, mean [TAMX] and maximum end-diastolic velocities, S/D ratio, RI, PI) and 10 threshold values per index (the 1st to 50th percentiles for the qualitative indices and the 50th to 99th percentiles for the quantitative indices). The following results were obtained (1) the development of chronic placental insufficiency was predicted best in Doppler examinations of the umbilical artery by calculating the PI with the 60th percentile as the threshold value, and in examinations of the uterine artery by determining the S/D ratio with the 90th percentile; 2nd (2) acute placental insufficiency was predicted best by calculating the mean blood flow velocity (TAMX) in the umbilical artery, with the 50th percentile as the ideal cutoff value; in examinations of the uterine artery the best results were obtained by determining the S/D ratio with the 90th percentile as cutoff value. Three conclusions may be drawn from the results: (1) taken overall, the qualitative Doppler parameters (S/D ratio, RI, PI) are superior to the quantitative parameters (maximum systolic, mean [TAMX] and maximum end-diastolic velocity) in the detection of both chronic and acute placental insufficiency; (2) in Doppler examinations of the umbilical artery the optimal threshold value is in the region of the 60th, and in examinations of the uterine artery in the region of the 90th, percentile; and (3) chronic placental insufficiency was detected better than the acute form; examinations of the umbilical artery yielded more explicit data than those of the uterine artery.