Available online 30 November 2023

The published reference ranges for Doppler parameters of the fetal pulmonary artery (PA) are usually derived from small sample sizes with no practical standard score or percentile ranking, which hinders systematic comparisons of Doppler figures across different gestational ages. This study aimed to establish comprehensive reference ranges and provide a percentile ranking solution for key spectral Doppler parameters.

This is a cross-sectional study of 465 uncomplicated, singleton pregnancies during 20 – 40 weeks of gestation. Spectral waveforms of the fetal main branch PA were obtained with pulsed-wave Doppler interrogation site within 5mm from the vascular origin. Fifteen spectral Doppler parameters were identified. Associations between these parameters with gestational age (GA) and fetal heart rate (FHR) were assessed and used to develop percentile calculators via different statistical models. Root mean squared error (RMSE) of each model was calculated to determine best performance solution.

Acceptable spectral waveforms were obtained for 94.1% (438/465) of the fetuses. All Doppler parameters except pulsatility index (PI), manual-traced PI, peak systolic velocity and time-to-systolic notch/acceleration time ratio were significantly correlated with GA, while acceleration time, ejection time, time to systolic notch, peak early-diastolic reversal flow and peak early-diastolic reversal flow/peak systolic velocity ratio were additionally significantly correlated with FHR. Support Vector Machine models with radial basis kernel yield the best percentile estimation (RMSE of 2.17-4.08 and R2 of >0.98). Furthermore, the top 5% and bottom 5% outliers could be identified with positive predictive values of 0.71-0.97. An online user interface of percentile calculators is available at https://github.com/cmb-chula/fetoPAD.

This study presents normal reference ranges and percentile calculators for 15 spectral Doppler parameters of the fetal main branch PA, some of which have not been published. The estimated percentiles enhance comparison and outlier detection of the spectral Doppler figures among fetuses at different gestational ages.

2023 Published by Elsevier Inc. on behalf of the American Society of Echocardiography.