Comparison between Three Methods of Fetal Weight Estimation during the Active Stage of Labor Performed by Residents: A Prospective Cohort Study.

OBJECTIVE: To compare the accuracy of ultrasonographic, calculated, and clinical methods for the estimation of fetal weight (EFW) performed during active labor by residents.

METHODS: Parturients in active labor underwent prospectively EFW by 3 methods: ultrasonographic, clinical, and calculated (extrapolating EFW from a previous scan). Three different blinded residents evaluated each woman. Background variables were examined for their effect on the accuracy of each method. Comparison of the methods for the detection of macrosomia and small for gestational age (SGA) was also performed.

RESULTS: Among the 405 women recruited, the rates of accuracy of ultrasonographic, clinical, and calculated EFW (within ±10%) was 72.5, 74.3, and 71.1%, respectively. The correlation coefficient between the methods and actual birth weight (ABW) were 0.702-0.611 (using 7 Hadlock formulas), 0.649, and 0.622, respectively (all p < 0.001). By logistic regression, epidural analgesia was associated with higher and second stage of labor with lower accuracy of ultrasonographic EFW. For the detection of macrosomia, clinical (p < 0.001) and calculated EFWs (p = 0.035) were superior to ultrasonographic EFW. For the detection of SGA, ultrasonographic EFW was superior to calculated (p < 0.001) and clinical (p < 0.001) EFWs.

CONCLUSION: All 3 methods performed by residents during labor correlated well with ABW. Clinical and calculated EFWs were superior for macrosomia detection, whereas ultrasonographic EFW was superior for SGA detection.