[Accuracy of ultrasound estimated fetal weight at term]

Our aim was to evaluate the accuracy of estimated fetal weight (EFW) by ultrasound at due date and the factors that could affect it.

We performed a retrospective study of 233 patients in 2014. An ultrasound was performed at due date consultation around 41 weeks of amenorrhea by midwives sonographer. EFW was calculated using the Hadlock's formula with 3 parameters (biparietal diameter, abdominal circumference and femur length) and then adjusted including the growth from the due date consultation to the day of delivery (25g/day) and finally compared to birth weight (BW).

The mean absolute weight difference between EFW adjusted and BW was 256g [0; 910]. The mean absolute percentage error was 7.2 % [0; 24.5] and the proportion of the EFW adjusted within 10 % of BW was 69.1 %. There was a strong correlation between EFW adjusted and BW (R=0.79). Obesity in early pregnancy or childbirth, excessive weight gain, the presence of oligoanamnios and fetal macrosomia had no influence on the estimated fetal weight. Indeed, the mean absolute percentage error of child who were macrosome and those were not, was similars (7.9 % vs 7.1 %, P=0.407).

EFW by ultrasound at due date is performant. However, the adjustment by the effect growth does not improve accuracy. Fetal macrosomia do not decrease the accuracy of ultrasound to estimate the fetal weight at term.