Profile of severely growth-restricted births undelivered at 40 weeks in Western Australia

Purpose: To investigate the proportion of severely growth-restricted singleton births < 3rd percentile (proxy for severe fetal growth restriction; FGR) undelivered at 40 weeks (FGR_40), and compare maternal characteristics and outcomes of FGR_40 births and FGR births at 37–39 weeks’ (FGR_37–39) to those not born small-for-gestational-age at term (Not SGA_37+). Methods: The annual rates of singleton FGR_40 births from 2006 to 2015 were calculated using data from linked Western Australian population health datasets. Using 2013–2015 data, maternal factors associated with FGR births were investigated using multinomial logistic regression to estimate odds ratios (OR) with 95% confidence intervals (CI) while relative risks (RR) of birth outcomes between each group were calculated using Poisson regression. Neonatal adverse outcomes were identified using a published composite indicator (diagnoses, procedures and other factors). Results: The rate of singleton FGR_40 births decreased by 23.0% between 2006 and 2015. Factors strongly associated with FGR_40 and FGR_37–39 births compared to Not SGA_37+ births included the mother being primiparous (ORs 3.13: 95% CI 2.59–3.79; 1.69, 95% CI 1.47, 1.94, respectively) and ante-natal smoking (ORs 2.55, 95% CI 1.97, 3.32; 4.48, 95% CI 3.74, 5.36, respectively). FGR_40 and FGR_37–39 infants were more likely to have a neonatal adverse outcome (RRs 1.70, 95% CI 1.41, 2.06 and 2.46 95% CI 2.18, 2.46, respectively) compared to Not SGA 37+ infants. Conclusions: Higher levels of poor perinatal outcomes among FGR births highlight the importance of appropriate management including fetal growth monitoring. Regular population-level monitoring of FGR_40 rates may lead to reduced numbers of poor outcomes.