ULTRASOUND-BASED PREDICTION OF NEONATAL BIRTH WEIGHT AT TERM USING FETAL BIOMETRY

Abstract

Background: Fetal weight assessment near delivery is central to obstetric risk stratification because both low birth weight and excessive fetal growth are associated with adverse maternal and neonatal outcomes. Ultrasound-based estimated fetal weight (EFW) is widely used in late pregnancy, but its clinical value depends on how closely the estimate reflects neonatal weight after birth.

Objective: To characterize the relationship between term ultrasound EFW and neonatal birth weight, with particular attention to gestational-age-specific patterns from 37 to 40 weeks.

Methods: A prospective comparative study was performed in a diagnostic ultrasound service in Islamabad, Pakistan. Pregnant women referred for late-gestation obstetric scanning were enrolled using non-probability sampling. Ultrasound examinations were performed on a MyLab 50 grayscale system with a 3-5 MHz transducer. Recorded fetal biometric variables included biparietal diameter, abdominal circumference and femur length, from which EFW was obtained. Birth weight was recorded after delivery. The planned sample size was 109, and 108 cases were included in the final analysis. Descriptive measures and t-test comparisons were used to examine EFW and birth weight overall and within gestational-age groups.

Results: The overall mean EFW was 3.3979 +/- 0.3173 kg and mean birth weight was 3.4089 +/- 0.4608 kg. The mean difference was -0.0110 kg, and the comparison was not statistically significant (p=0.838). The subgroup table included 44 women at 37 weeks, 36 at 38 weeks, 25 at 39 weeks and 3 at 40 weeks. Mean EFW versus birth weight was 3.2736 versus 3.3205 kg at 37 weeks, 3.4375 versus 3.4733 kg at 38 weeks, 3.5472 versus 3.4728 kg at 39 weeks and 3.5000 versus 3.4000 kg at 40 weeks. The comparisons at 37, 38 and 39 weeks were also non-significant.

Conclusion: At the level of group means, term ultrasound EFW closely approximated neonatal birth weight in this cohort. The findings support the clinical usefulness of late-pregnancy sonographic biometry while also emphasizing that mean-level agreement does not quantify individual prediction error. Future work should use paired agreement methods, prespecified EFW equations and scan-to-delivery intervals to determine individual-level accuracy.