Two‐Dash Line

OBJECTIVES There has been a dearth of an accurate and reliable method for the measurement of fetal pelvic bones. In this study, we describe a novel, easy-to-use method for ischial and iliac bone measurement in fetal ultrasound scanning. METHODS This prospective cross-sectional study was performed on 1179 pregnant women at 12 to 40 weeks of an uneventful gestation. Pelvic biometric indices, including the length of the ilium and ischium, were measured by a novel and easy method. Then data were analyzed by regression models to develop a formula for gestational age (GA) estimation based on pelvic bones. RESULTS The approximate ossification time of the ischium was determined to range between the 13th and 20th gestational weeks. We calculated 3 formulas using linear regression models: formula 1, GA (days) = 92.563 + (11.604 × ischial length); formula 2, GA (days) = 57.006 + (7.819 × iliac length); and formula 3, GA (days) = 65.809 + (5.610 × iliac length) + (3.431 × ischial length). CONCLUSIONS The 2-dash line method can contribute to efficient and precise ultrasound measurement of the ilium and ischium in pelvic biometry of the fetus.