Reference values for ductus venosus Doppler velocity indices between 11 and 13+6 weeks of gestation: A single-center prospective study in Iran

Background: This study aimed to investigate reference Doppler velocimetry indices (DVIs) of the fetal ductus venosus (DV) during 11-13 + 6 gestational weeks. Materials and Methods: In a prospective observation over referrals to a single tertiary care center in a 2-year interval, normal singleton pregnancies with fetal crown-rump lengths (CRLs) of 43-80 mm were examined by a single experienced sonographer for their DV pulsatility index (DVPI), DV resistance index (DVRI), and S-wave maximum velocity/A-wave minimum velocity (S/A ratio). Multinomial and quantile regression functions were used to analyze the effect of gestational age (estimated by CRL) on reference values (5(th) and 95(th) percentiles of the distribution in each gestational day/week). P < 0.05 was considered significant. Results: Over a sample of 415 participants with a mean/median gestational age of 12 + 1 weeks, no significant correlations were found between the CRL and DVIs using multinomial regression functions (linear model best fitted for all [DVPI: B coefficient = 0.001, P = 0.235] [DVRI: B coefficient = 0.001, P = 0.287] [DV S/A: B coefficient = 0.010, P = 283]). Quantile regression analyses of DVIs' reference values were nonsignificant across the CRL range except for the DVRI ([5(th) regression line: coefficient = -0.004, P = 0.018] [95(th) regression line: coefficient = -0.001, P = 0.030]). Conclusion: Reference values for DVPI, DVRI, and DV S/A ratios were established as 0.80-1.39, 0.62-0.88, and 2.57-6.70, respectively. Future meta-analyses and multicenter studies are required to incorporate DV DVIs into an updated universal version of the practice.