Establishing Reference Ranges for Doppler Parameters of the Fetal Aortic Isthmus in the Third Trimester

Objective: This study evaluated the significance of Doppler indices of the fetal aortic isthmus in diagnosing fetal hemodynamic disorders early. The aim was to determine the Doppler values within the fetal aortic isthmus in the third trimester of pregnancy. Materials and Methods: Patients who presented with pregnancies between 28 and 40 weeks of gestation were examined for Doppler indices of the fetal aorta and compared with the gestational age. Among these, 325 normal fetuses (mean gestational age, 25 weeks) were included in the study. The correlation between Doppler indices and gestational age was evaluated using regression equations. Linear, quadratic, and cubic models were applied to all the variables. Results: Curve estimation analysis showed that peak systolic velocity ( R 2 = 0.168), end-diastolic velocity ( R 2 = 0.042), pulsatility index ( R 2 = 0.101), and time-averaged maximum velocity ( R 2 = 0.090) correlated with gestational age (cubic model, p < .001). However, S/D, resistance index, and isthmic systolic index were not significantly correlated with gestational age. Notably, the R 2 values were low for all variables. Conclusion: In this fetal cohort, the suggested normal reference values for Doppler indices based on gestational age in the third trimester of pregnancy were determined.