Bulgarian Federation of Obstetrics and Gynecology (BFOG) amniotic fluid index charts

Introduction: Amniotic fluid plays a critical role in fetal development, particularly for the lungs, musculoskeletal, and urinary systems. Traditional international nomograms for the amniotic fluid index (AFI) are often based on data from heterogeneous populations and do not accurately reflect specific characteristics of the local population. The lack of local reference values for AFI may lead to diagnostic inaccuracies and unnecessary medical interventions. This study aims to establish local reference ranges for AFI in the Bulgarian population, providing a more accurate assessment of amniotic fluid levels. Materials and Methods: Between 2021 and 2024, a multicenter, longitudinal observational study was conducted including 1,559 singleton pregnancies in Bulgaria. Follow-up was performed between the 26th and 40th gestational weeks with ultrasound measurements taken every two weeks. The AFI assessment methodology involved dividing the uterus into four quadrants, with all measurements performed by certified specialists. Nonparametric quantile regression was used to calculate percentile values for AFI in data processing. Results: The results indicate that the average amniotic fluid volume in the Bulgarian population remains relatively constant from the 26th to the 40th gestational week, while the 95th percentile increases up to 25.5 near term. The lower AFI limit (5th percentile) is higher than internationally recommended values, highlighting characteristics specific to the Bulgarian population that warrant consideration. Conclusions: Establishing local reference values for AFI ensures more precise diagnostics and improves the quality of prenatal care. These values allow for timely detection of fetal development abnormalities and reduce the risk of unnecessary interventions. Local reference values support personalized medical care tailored to the specific characteristics of the Bulgarian population.