Perinatal Outcomes in Large Infants Using Customised Birthweight Centiles and Conventional Measures of High Birthweight

Background: Large‐for‐gestational‐age (LGA) or macrosomic infants are associated with adverse maternal and neonatal outcomes. It is unclear if these associations are stronger using customised birthweight centiles. We compared outcomes between term infants defined macrosomic by birthweight >4000 g (Macro₄₀₀₀) or LGA by population centiles (LGA_pop) with those defined LGA by customised centiles (LGA_cust). Methods: This is a prospective cohort study of 2668 term nulliparous women recruited into the Screening for Pregnancy Endpoints (SCOPE) study centres in Auckland, New Zealand and Adelaide, Australia. Maternal (caesarean delivery, postpartum haemorrhage) and infant (severe neonatal morbidity/mortality and admission to neonatal intensive care) outcomes in Macro₄₀₀₀ and LGA groups were compared with appropriate‐for‐gestational‐age infants by customised centiles using logistic regression. Results: Customised centiles defined fewer infants as LGA (10.3% LGA_cust, 14.8% Macro₄₀₀₀, 11.2% LGA_pop). However customised centiles showed stronger association with adverse outcomes. Pre‐labour and intrapartum caesarean section were increased twofold in LGA_cust pregnancies, including those that were not Macro₄₀₀₀ or LGA_pop. Postpartum haemorrhage was increased twofold in mothers of LGA_cust infants only when infants were also LGA_pop. Severe neonatal morbidity/mortality or admission to neonatal intensive care was increased twofold in LGA_cust who were also either Macro₄₀₀₀ or LGA_pop. Importantly 52.3% of Macro₄₀₀₀ and 25.5% of LGA_pop infants were AGA_cust and not at increased risk of most adverse maternal or neonatal outcomes. Conclusions: The use of customised centiles are more strongly associated with adverse birth outcomes and its use should be considered in the definition of LGA.