Bulgarian Federation of Obstetrics and Gynecology (BFOG) reference ranges for MCA PI and PSV

Introduction: The assessment of fetal well-being is a key aspect of prenatal care. Doppler velocimetry of the middle cerebral artery (MCA), particularly the calculation of the Pulsatility Index (PI) and Peak Systolic Velocity (PSV), are well-established methods for monitoring fetal hemodynamics. The accurate interpretation of these values requires reference ranges specific to the given population. The lack of such reference data for the Bulgarian population motivated the present study. Materials and Methods: Between 2022 and 2024, we conducted a prospective, observational, cross-sectional study involving 725 low-risk singleton pregnancies between the 28th and 40th gestational weeks. All pregnancies were dated based on last menstrual period (LMP) and/or ultrasound measurement of the crown-rump length (CRL) in the first trimester. Pregnancies with complications, fetal anomalies, and multiple gestations were excluded. Measurements of MCA PI and PSV were performed by certified specialists following a standardized protocol. For each gestational week, we calculated the median, 5th, and 95th percentiles of the listed modalities. Results: Based on the collected data, we established reference ranges for MCA PI and MCA PSV in the Bulgarian population. Comparative analysis with other established nomograms revealed significant differences in the numerical values of both parameters across different gestational weeks. Conclusions: The development of local reference ranges for MCA PI is an essential prerequisite for more accurate calculation of the cerebro-placental ratio (CPR)—a key indicator for fetal well-being in the third trimester. Furthermore, analyzing variations in MCA PSV within the Bulgarian population enables a more precise diagnosis of fetal anemia during intrauterine development.