Placental Assessment Using Microvascular Flow Imaging: Reference Ranges and Clinical Application

Objectives To establish gestational age‐specific reference ranges for the intraplacental vascular index measured using microvascularity‐flow ultrasound software (VI MV ) and to evaluate its variation by placental location, parity, and pregnancy outcome. Methods This prospective study enrolled 354 singleton pregnancies, of which 243 (68.64%) uncomplicated cases were used to construct reference ranges. A residual bootstrap method with 500 iterations was applied to square‐root–transformed VI MV values, followed by back‐transformation to derive the 5th, 50th, and 95th percentiles with 95% confidence intervals. Group differences were assessed using quantile regression, and associations with Doppler parameters were examined. Results VI MV increased significantly with advancing gestational age (linear coefficient 1.88, p = .007), following a curvilinear pattern with mild late‐gestation downturn (quadratic coefficient − 0.036, p = .011). Posterior placentas showed slightly higher early values, although this difference was not significant; from 31 weeks onward, anterior placentas demonstrated significantly higher VI MV (mean difference + 15.4, p = .010 at 31–35 weeks; +11.6, p = .003 at 36–40 weeks). Multiparous women showed a modestly higher fitted trajectory and a similar non‐significant trend toward higher birthweight, but parity was not independently associated with VI MV . Pregnancies complicated by maternal disease, hypertensive disorders, or small‐for‐gestational‐age neonates exhibited lower trajectories than uncomplicated pregnancies, although these differences were not statistically significant. VI MV was inversely associated with uterine and umbilical artery pulsatility indices and positively associated with umbilical vein time‐averaged mean velocity. Conclusions Gestational age–specific VI MV reference ranges were established. VI MV may provide an adjunctive quantitative marker for assessing placental vascular adaptation and identifying pregnancies with altered placental perfusion.