Why we miss fetal growth restriction: Identification of risk factors for severely growth-restricted fetuses remaining undelivered by 40 weeks gestation

Abstract

Background: Severe fetal growth restriction (FGR) is a leading cause of adverse perinatal morbidity and mortality; however, in Victoria, 35% of severely growth-restricted infants are undelivered by 40 weeks gestation. Aims: We aimed to identify factors associated with failure to deliver severely growth-restricted fetuses by 40 weeks gestation. Methods: We conducted a retrospective case-control study of term singletons born <3rd centile for gestation at a single tertiary centre (2010–2017). Infants with a planned delivery for FGR between 37.0–39.6 weeks gestation (‘planned birth’ group; n = 187) were compared with those undelivered by 40.0 weeks (‘undelivered’ group; n = 233). Variables assessed included the presence of risk factors for FGR, model of care, symphyseal-fundal height measurements and third trimester ultrasounds. Results: An equivalent proportion of women were ‘high-risk’ for FGR on history (31.3% vs 38.0%, P = 0.187) in the planned and undelivered groups. Women booked under low-risk models (shared care and midwifery-led care) were significantly more likely to be in the undelivered group compared to those booked under traditional collaborative models (79.8% vs 37.4%, P < 0.001). Women in the undelivered group were less likely to have received a third trimester ultrasound (93.0% vs 40.3%, P < 0.001); however, they were more likely to have had a reassuring ultrasound with an estimation of fetal weight or abdominal circumference >10th centile (78.7% vs 16.1%, P < 0.001). Conclusions: Failure to deliver the severely growth-restricted fetus before 40.0 weeks is more likely to occur in the following situations: (i) failure to receive an indicated third trimester ultrasound; (ii) the presence of falsely reassuring third trimester ultrasound scan; and (iii) booking under a low-risk rather than traditional collaborative models of care.