Reference Ranges for the Pulsed wave Doppler of the Fetal Cardiac Inflow and Outflow Tracts from 13 to 36 Weeks Gestation: Short title: Zidere, Fetal inflow and outflow tract, Pulsed wave Doppler, z scores.

Abstract Objective Doppler assessment ventricular filling and outflow tract velocities are an integral part of the fetal echocardiogram, to assess diastolic function, systolic function and outflow tract obstruction. There is a paucity of prospective data from a large sample of normal fetuses in the published literature. We report reference ranges for pulsed wave Doppler flow of the mitral valve, tricuspid valve, aortic valve and pulmonary valve as well as heart rate, in a large number of fetuses prospectively examined at a single tertiary fetal cardiology centre. Methods The study population comprised 7885 fetuses at 13 to 36 weeks’ gestation with no detectable abnormalities from pregnancies resulting in normal live births. Prospective pulsed wave Doppler blood flow measurements were taken of the mitral, tricuspid, aortic and pulmonary valves. The fetal heart rate was recorded at the time of each assessment. Regression analysis, with polynomial terms to assess for linear and nonlinear contributors, was used to establish the relationship between each measurement and gestational age. Results The measurement for each cardiac Doppler measurement was expressed as a z score (difference between observed and expected value divided by the fitted SD corrected for gestational age) and percentile. Analysis included calculation of gestation-specific SDs. Regression equations are provided for the cardiac inflow and outflow tracts. Conclusions The study establishes reference ranges for fetal cardiac Doppler measurements and heart rate between 13 to 36 weeks’ gestation that may be useful in clinical practice.