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

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+).

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).

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.

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.