Burak BAYRAKTAR
Journal of Health Sciences and Medicine - 2026;9(5):1418-1426
Aims: This study aimed to establish gestational age-specific reference ranges, nomograms, and z-score equations for aortic isthmus (AoI) Doppler parameters between 18 and 24 weeks of gestation and to assess their relationships with fetal biometry and arterial Doppler measurements. Methods: In this prospective cross-sectional study, 165 uncomplicated singleton pregnancies undergoing routine second-trimester anatomical assessment (18+0-24+0 weeks) were included. Pulsed-wave Doppler ultrasonography was used to measure AoI peak systolic velocity (AoI PSV), end-diastolic velocity, time-averaged maximum velocity (AoI TAMAX), time-averaged mean velocity, pressure gradients, pulsatility index (AoI PI), resistance index (AoI RI), and systolic-to-diastolic ratio (AoI S/D). Reference ranges, percentile values, regression equations, and z-score models were generated. Correlations with fetal biometric parameters and umbilical artery (UA) and middle cerebral artery (MCA) Doppler indices were analyzed. Results: AoI PSV and AoI TAMAX showed significant increases with advancing gestation (p<0.05), whereas AoI PI, AoI RI, and AoI S/D remained relatively stable. Mean AoI PSV increased from 59.69+/-11.84 cm/s at 18 weeks to 75.11+/-17.05 cm/s at 24 weeks. Weak but significant positive correlations were observed between AoI PSV, AoI TAMAX, pressure-gradient measurements, and fetal biometric parameters (all p<0.05). UA end-diastolic velocity demonstrated weak positive correlations with several AoI parameters, while no significant associations were identified between AoI measurements and MCA Doppler indices. Conclusion: This study provides gestational age-specific reference ranges, nomograms, and z-score equations for a comprehensive set of fetal aortic isthmus Doppler parameters. AoI velocity parameters demonstrated modest gestational age-related increases, whereas impedance indices remained relatively stable.
