Placental blood flow measured by three-dimensional power Doppler ultrasound at 26 to 35 weeks gestation in normal pregnancies

Objective. To evaluate placental vascular indices, in pregnancies between 26 and 35 weeks, using three-dimensional power Doppler (3DPD) ultrasound and the effect of placental location on these indices. Methods. This was a cross-sectional study involving 283 patients. The placental vascularization index (VI), flow index (FI) and vascularization and flow index (VFI) was obtained using the VOCAL program. Pearson's linear correlation coefficient was used to assess the relationship between gestational age and these indices. Student's parametric t-test and Levene's test were used to analyse the results between VI, FI and VFI and placental location. Results. There was no linear correlation between gestational age (GA) and VI (p = 0.390) and VFI (p = 0.053). Only the FI presented a significant linear correlation (p = 0.004), with a slow increase according to GA. It was possible to construct a reliable nomogram only for this index. There were no significant differences in the VI, FI and VFI according to placental location (p = 0.323, 0.172 and 0.120, respectively). Conclusion. Placental FI assessed by 3DPD increases progressively and significantly between 26 and 35 weeks. Placental location has no influence on the three vascular indices studied. The FI reference values obtained in this study can be used as a parameter for future investigations on placental vascularization using 3DPD.