Ultrasound estimation of fetal weight in small for gestational age pregnancies

Approximately half of small for gestational age (SGA) cases are due to maternal or fetal pathology, and may result in significant neonatal morbidity and mortality. The estimated fetal weight (EFW) measurement is the cornerstone of ultrasonographic findings when diagnosing and managing SGA pregnancies. Our objective was to determine the ultrasound accuracy of EFW in SGA pregnancies.

A retrospective chart review was performed of all pregnancies complicated by SGA from a single institution (Stanford University) over a 2-year-period (2004-2006). SGA was defined as EFW < or = 10%. 98 neonates whose last ultrasound for EFW occurred within 7 days of delivery were included in the study. The absolute differences between the EFW and birthweight (BW) were analyzed, and the absolute percent errors were calculated as (EFW - BW)/BW x 100. The mean absolute differences and mean absolute percent errors were analyzed across all gestational ages (GA) and EFWs using one-way analysis of variance.

The mean absolute percent error for the entire cohort was 8.7% (+/-6.3%). There was no statistically significant difference in the mean absolute percent error across all GAs (<32 weeks, 32-36 weeks, >36 weeks), and EFWs (<1500 g, 1500-2000 g, >2000 g).

Ultrasound measurement of EFW in SGA pregnancies is consistent across all GAs and EFW measurements.