Development of Gestational Age–Specific Reference Charts for Fetal Doppler Indices Between 24 and 40 Weeks of Gestation

Background The objective of this study was to develop gestational age–specific reference charts for fetal Doppler indices, including the umbilical artery, middle cerebral artery, and cerebroplacental ratio, between 24 and 40 weeks of gestation in normal singleton pregnancies. Using standardized Doppler measurements and quantile regression analysis, the study aimed to establish locally relevant percentile curves based on data from Tu Du Hospital. These reference charts are intended to support accurate assessment of fetal and placental hemodynamics in Vietnamese clinical practice. Method This cross-sectional descriptive study was conducted at Tu Du Hospital, Ho Chi Minh City, Vietnam, from February 2026 to February 2028. Low-risk singleton pregnancies between 24 and 40 weeks of gestation with reliable gestational age dating were included. Pregnancies with maternal medical disorders, fetal anomalies, fetal growth restriction, or inadequate Doppler image quality were excluded. Fetal Doppler ultrasound was performed according to ISUOG guidelines. Pulsatility index measurements of the umbilical artery and middle cerebral artery were obtained, and the cerebroplacental and umbilicocerebral ratios were calculated. Each Doppler parameter was measured at least three times, and the mean value was used for analysis. Gestational age–specific reference values and percentile curves were generated using quantile regression. Statistical analyses were performed using SPSS software, with p < 0.05 considered statistically significant. The study protocol and all related materials received approval from the Ethics Committee of Tu Du Hospital (Approval Number). Results The study included a large sample of low-risk singleton pregnancies between 24 and 40 weeks of gestation. The estimated minimum sample size was 384 cases per gestational week, corresponding to approximately 6,528 cases across 17 weeks (24–40 weeks), with an additional 10% allowance for non-eligible or incomplete data. Umbilical artery pulsatility index (UA-PI) showed a progressive decline with advancing gestational age. Middle cerebral artery pulsatility index (MCA-PI) demonstrated a mild gestational age–related decrease, particularly in late gestation. The cerebroplacental ratio (CPR) and umbilicocerebral ratio (UCR) exhibited gestational age–dependent distributions. Gestational age–specific percentile curves were successfully constructed using quantile regression. Conclusion This study provides gestational age–specific reference charts for fetal Doppler indices derived from a large sample of normal pregnancies at Tu Du Hospital. The charts can serve as a valuable local standard for evaluating fetal and placental circulation, supporting early identification of abnormal Doppler patterns in high-risk pregnancies.