Accuracy of ultrasonic fetal weight estimation using head and abdominal circumference and femur length

Introduction Former investigations have shown that the accuracy of fetal weight estimation is significantly higher if several ultrasonic fe­tal parameters are measured, because the total body mass depends on the size of fetal head, abdominal circumference and femur length. The aim of this investigation was to establish the best regression model, that is a number of combinations of fetal parameters providing the most accurate fetal weight estimation in utero in our population. Material and methods This prospective study was carried out at the Gynecology and Obstetrics Clinic of the Clinical Center Novi Sad. It included 270 pregnant women with singleton pregnancies within 72 hours of delivery who underwent ultrasound measurements of the biparietal diameter (BPD), head circumference (HC), ab­dominal circumference (AC) and femur length (FL). Results In regard to fetal weight estimation formulas, the deviation was lowest using regression models that simultaneously analyzed four fetal parameters (0.55%) with SD ±7.61%. In these models the estimates of fetal weights were within ±5% of actual birth weight in 48.89%, and within ±10% of actual birth weight in 81.48%. Good results were also obtained using AC, FL measurements (0.92% ± 8.20) as well as using AC, HC, FL measurements (-1.45% ± 7.81). In our sample the combination of AC and FL model gave better results in fetal weight estimation (0.92 ± 8.20%) than the one using BPD and AC (2.97 ± 8.83%). Furthermore, the model using parameters AC, HC and FL showed a lower error in accuracy (-1.45 ± 7.81%) than the model using BPD, AC and FL (2.51 ± 7.82%). Conclusion This investigation has confirmed that the accuracy of fetal weight estimation increases with the number of measured ultra­sonic fetal parameters. In our population the greatest accuracy was obtained using BPD, HC, AC and FL model. In cases when fast estimation of fetal weight is needed, AC, HC, FL model may be appropriate, but if fetal head circumference cannot be measured (amnion rupture and/or fetal head already in the pelvis) the AC, FL model should be used.