Objectives: To compare the INTERGROWTH-21st and the WHO fetal growth chart in detecting term small for gestational age (SGA) neonates and predicting short-term adverse perinatal outcomes.

Design: A retrospective cohort study.Setting Department of Obstetrics and Gynaecology at the Aga Khan University Hospital Karachi.

Subjects: Term singleton pregnancies between July and December 2018 with ultrasound growth scan done within 4 weeks of delivery. Pregnancies with structural and chromosomal abnormalities and multiple gestations were excluded.

Outcome: The estimated fetal weight (EFW) was calculated using the INTERGROWTH-21st and the WHO fetal growth chart based on ultrasound measurements. Fetuses with EFW below the 10th percentile were classified as SGA. Neonates were confirmed as SGA based on similar postnatal weight percentile. Short-term adverse perinatal outcomes were also analysed.

Results: A total of 932 records were screened, and 478 were included in the analysis. The sensitivity of the WHO fetal growth chart (70.2%; 95% CI: 60.4%, 78.8%) was higher than the INTERGROWTH-21st (45.2%; 95% CI: 35.4%, 55.3%) for predicting neonatal SGA. The WHO fetal growth chart predicted more SGA neonates when compared with the INTERGROWTH-21st (AUC=0.75, 95% CI: 0.71, 0.80 and AUC=0.63, 95% CI: 0.58, 0.68, respectively). Both charts were similar in predicting the short-term adverse perinatal outcomes; AUC (95% CI) was 0.77 (0.70, 0.83) for INTERGROWTH-21st and 0.78 (0.72, 0.85) for the WHO fetal growth chart.

Conclusion: The WHO fetal growth chart demonstrates significantly better accuracy in predicting term SGA neonates compared with INTERGROWTH-21st. Further, both charts have similar prediction abilities for short-term adverse perinatal outcomes.