Spectral Doppler Parameters of Fetal Main Branch Pulmonary Artery at 20 to 40 Weeks of Gestation: Reference Ranges and Percentile Calculators.

BACKGROUND: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 (GAs). This study aimed to establish comprehensive reference ranges and provide a percentile ranking solution for key spectral Doppler parameters. METHODS:This is a cross-sectional study of 465 uncomplicated singleton pregnancies during 20 to 40 weeks of gestation. Spectral waveforms of the fetal main branch PA were obtained with a pulsed-wave Doppler interrogation site within 5 mm from the vascular origin. Fifteen spectral Doppler parameters were identified. Associations between these parameters with GA and fetal heart rate were assessed and used to develop percentile calculators via different statistical models. The root mean squared error of each model was calculated to determine the best performance solution. RESULTS:Acceptable spectral waveforms were obtained for 94.1% (438/465) of the fetuses. All Doppler parameters except pulsatility index, manually traced pulsatility index, 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 fetal heart rate. Support vector machine models with radial basis kernel yield the best percentile estimation (root mean squared error 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 to 0.97. An online user interface of percentile calculators is available at https://github.com/cmb-chula/fetoPAD. CONCLUSIONS: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 GAs.