Accuracy of sonographic fetal weight estimation in full-term singleton pregnant women

Objectives: To investigate the factors which might influence the sonographic fetal weight estimation (SFWE) accuracy.

Methods: This prospective study was conducted among 949 singleton term pregnant women who delivered at a tertiary center, from January 2017 to December 2017. All participants' maternal (i.e. parity, age, body mass index and gestational weight gain during pregnancy), fetal sonographic (i.e. fetal presentation, amniotic fluid index, localization of placenta and estimated fetal weight) and neonatal (birth weight and gender) characteristics were recorded. A p<0.05 was considered significant.

Results: The mean absolute percent error (APE) values of SFWE was 8.2±6.5 percent, and overall failure ratio (APE >10%) was 33%. In failure group, primiparous woman and cephalic presentation fetus were significantly more common compared to accuracy group (55.9% vs.44.8%; p=0.001 and 98% vs. 95.2%; p=0.03, respectively). In contrast, the mean neonatal birth weight (NBW) value was significantly lower in failure group compared to success group (3250±565 gr vs. 3404±410 gr; p=0.001). The correlation between SFWE and NBW was linear, however negative, and significant (p=0.001). Logistic regression analysis revealed that primiparous woman, cephalic presentation fetus and <3300 gr NBW were independent risk factors for the SFWE failure (relative risks were 1.6, 2.8 and 2.4 respectively, p<0.05).

Conclusion: SFWE has a high correlation with NBW, however it's accuracy is still unsatisfactory, and depend on many unpredictable and inconsistent factors.