Accuracy of Intrapartum Fetal Weight Estimation Using Dare's Formula and Transabdominal Ultrasonography in Pregnant Women with Normal and High Prepregnant BMI at Maharat Nakhon Ratchasima Hospital

Objectives: To compare the accuracy of clinical fetal weight estimation using Dare's formula and sonographic estimation using Hadlock's formula in pregnant women with normal and high prepregnant BMI. Materials and Methods: This prospective cohort study was conducted at Maharat Nakhon Ratchasima Hospital, Thailand between July 2019 to November 2019. Term singleton pregnant women whose prepregnant body mass index (BMI) was 18.5 kg/m2 or greater were included. Maternal BMI was divided into normal BMI (18.5 - 23.0 kg/m2) and high BMI (≥ 23.0 kg/m2) for Asian population. Symphysis-fundal height and abdominal circumference was measured, followed by performing sonographic estimation using Hadlock's formula by second-year residents. The primary outcome was the accuracy rate defined by the absolute percentage error of estimated fetal weight < 10 percent. Results: 205 pregnant women were recruited. Overall accuracy of clinical estimation and sonographic estimation was 52.7% and 80.0% (p < 0.001). In normal BMI group, the accuracy was similar between two methods (p = 0.143). In high BMI group, sonographic estimation was more accurate than clinical estimation (77.8% vs 36.8%, p < 0.001). Conclusion: Sonographic estimation can be used to estimate fetal weight in pregnant women with normal and high prepregnant BMI group with acceptable accuracy. However, clinical estimation may reliably substitute sonographic estimation among pregnant women with normal BMI group in the condition that transabdominal ultrasonography is not accessible.