Performing a routine ultrasound on pregnant women with obesity in their third trimester is of limited utility in identifying aberrant fetal growth, Australian researchers report.

The findings have important implications for clinical practice, because doctors need to be aware of how poorly the scan — recommended in RANZCOG guidelines — predicts babies who are small or large for gestational age (SGA and LGA), the authors say.

The researchers from Western Health, in Melbourne, carried out a retrospective analysis of 1008 pregnancies with maternal BMI of 35kg/m² or higher who underwent such a scan at one tertiary centre.

All women included in the study were scanned between 34+0 and 36+6 weeks’ gestation, in line with Victorian government recommendations, with results of the latest scan being used in the analysis for women who had multiple scans.