The significance of increasing umbilical artery systolic-diastolic ratios in third-trimester pregnancy

Objective: To evaluate the clinical significance of a marked increase in the systolic-diastolic ratios (S/Ds) of the umbilical artery (UA) Doppler velocity waveforms of third-trimester fetuses. Methods: We evaluated 552 pregnancies at risk for placental insufficiency. Each patient had at least five successive weekly UA Doppler velocimetry studies between 32–42 weeks and a highest S/D within the normal range for gestational age. The S/D was considered markedly increased if it was at least 20% higher than the mean of four previous values. Clinical end points reviewed included mortality, fetal distress, 5-minute Apgar score below 7, metabolic acidosis, and neonatal intensive care unit (NICU) admissions for reasons other than prematurity. Results: The S/Ds were normal in 478 patients and were markedly increased in 74. The two groups were similar in mean gestational age at testing and delivery and in the rates of fetal growth retardation and low 5-minute Apgar scores. The group without increased S/Ds had a higher mean birth weight and lower incidences of perinatal death, cesarean delivery for fetal distress, acidosis, and NICU admission. The overall sensitivity (43%), specificity (90%), positive predictive value (27%), and negative predictive value (95%) were similar to our previous experience in which we used a criterion of S/D above the 90th percentile. Conclusion: Marked increases in UA S/Ds, even if within an institutional “normal” range, may indicate a fetus at increased risk of compromise.