Reference values for pulsatility index of fetal anterior and posterior cerebral arteries in prolonged pregnancy

Objective: To establish consistent normal reference values for fetal anterior cerebral artery (ACA) and posterior cerebral artery (PCA) pulsatility index (PI) in prolonged pregnancy. Methods: This prospective cross-sectional observational study included singleton normal prolonged pregnancies into two study groups according to the gestational age: from 40 + 0 to 40 + 6 and from 41 + 0 to 41 + 6 weeks. The PI was assessed in both anatomical segments of ACA (ACA-S1 and ACA-S2) and of PCA (PCA-S1 and PCA-S2) with color Doppler imaging and pulsed Doppler examination, and reference centiles charts were generated. PI values from the two investigated segments of each vessel were also compared. Results: Data were obtained in 771 patients: n = 448 in the 40 + 0 and 40 + 6 weeks group, and n = 323 in the 41 + 0 and 41 + 6 weeks group. A moderate decrease in PI was observed as pregnancy progressed. No differences in PI values were found between the two anatomical segments of ACA and PCA. Conclusion: This study provides Doppler reference values for the fetal ACA and PCA PI. It also shows that Doppler examination could be performed indifferently in one of the two anatomical segments of these arteries.