Reference ranges, nomograms, and z-score equations for fetal aortic isthmus Doppler parameters during second-trimester anatomical assessment: a prospective cross-sectional study

Abstract

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