Objective: To assess the impact of implementation of GAP in a multi-ethnic population with high obesity and high deprivation. Design/Methods: Retrospective before (2012) and after (2017) study (pre-and post-GAP). Outcomes were compared between epochs with adjustment for New Zealand Deprivation Index, maternal body mass index, ethnicity, cigarette smoking and age. Setting: Counties Manukau tertiary maternity facility, Auckland, New Zealand Population: Singleton, non-anomalous pregnancies, booked with a hospital midwife by 20 weeks’ gestation, with birth after 24 weeks’ gestation. Main Outcome Measures: Antenatal detection of SGA babies (<10th customised centile), labour induction, caesarean section and composite adverse neonatal outcome (neonatal unit admission >48 hrs, 5-minute Apgar Score <7, any ventilation). Results: Antenatal detection of SGA increased after introduction of GAP from 22.9% to 57.9% (aOR=4.81, 95% CI 2.82, 8.18) with similar SGA rates across epochs (13.8% vs 12.9%; p=0.68). Induction of labour and caesarean birth increased between epochs, but this increase was similar in SGA and non-SGA. Amongst SGA, increased antenatal identification post-GAP appeared to be associated with lower composite adverse neonatal outcome (identified SGA: pre-GAP 32.4% vs post-GAP 17.5%, aOR=0.44, 95% CI 0.17, 1.15; non-identified SGA: pre-GAP 12.3% vs post-GAP 19.3%, aOR=1.81, 95% CI 0.73, 4.48; interaction p=0.03). Conclusions: GAP was associated with an almost 5-fold increased likelihood for SGA detection, without significant increase in maternal intervention and some evidence of a reduction in composite adverse neonatal outcome in identified SGA pregnancies. GAP is a safe, effective tool for SGA detection in an ethnically diverse population with high obesity levels.