Three Methods of Fetal Weight Estimation Compared in Women With BMI ≥ 35 kg/m ² at Term—A Prospective Observational Study

Objective To compare sonographic, maternal, and clinical estimations of fetal weight in women with severe and morbid obesity (BMI ≥ 35 kg/m 2 ) at term. Methods We conducted a prospective study on multiparous women with singleton term pregnancies. We analyzed absolute error, absolute percentage error, and rates of error > 10%, > 15%, and > 20%; and error > 500 g for each method. Results Our study included 103 women with a median pre‐delivery BMI of 37.9 (35.0–50.4) kg/m 2 . Clinical estimation showed a higher mean error than maternal estimation (140.1 vs. −51.6 g, p < 0.001). The absolute error was comparable for the sonographic and maternal estimations (209 and 210 g, respectively); these values were lower ( p = 0.02) than that of clinical estimation (250 g). For sonographic estimation, the absolute percentage error was lower than for the clinical estimation (6.0% vs. 7.5%, p = 0.018). Similarly, for the maternal estimation, the absolute error was lower than for the clinical estimation (6.3% vs. 7.5%, p = 0.005). A greater proportion of women exhibited an absolute percentage rate error exceeding 15% with clinical estimation than with maternal estimation (15.1% vs. 2.9%, p = 0.002). A higher proportion of women displayed an absolute percentage rate error exceeding 20% with clinical estimation than with sonographic estimation (7.8% vs. 1.0%, p = 0.016) and with maternal estimation (7.8% vs. 0%, p = 0.008). Conclusion In women with a BMI ≥ 35 kg/m 2 , sonographic weight estimation and maternal estimation showed similar levels of accuracy, and both surpassed that of clinical estimation. Our findings demonstrate the potential utility of maternal estimation as an additional tool supporting the standard use of ultrasound. Trial Registration ClinicalTrials.gov identifier: NCT05478798