Risk factors for mortality and severe morbidity in fetuses with normal late third-trimester scan: population-based cohort study

Objective To identify antepartum risk factors for fetal or neonatal mortality and severe morbidity in pregnancies undergoing a universal late third-trimester ultrasound scan in which there was no ultrasound evidence of small-for-gestational age (SGA) or fetal growth restriction (FGR). Methods This was a retrospective population-based cohort study of singleton, non-anomalous term pregnancies undergoing a universal ultrasound scan at 35 + 1 to 36 + 6 weeks' gestation at a major UK maternity unit, over a period of 7 years. Pregnancies complicated by SGA or FGR were excluded. The outcomes were: stillbirth; severe composite adverse outcome, including extended perinatal mortality and severe morbidity; and severe SGA, defined as birth weight < 3(rd) centile. Potential clinical, demographic and ultrasonographic risk factors were evaluated using univariate and multivariate logistic regression analysis. Results The study population of 40 169 pregnancies comprised 88.9% of all eligible term pregnancies. There were 48 (0.1%) stillbirths, 221 (0.6%) cases of severe composite adverse outcome and 295 (0.7%) cases of severe SGA. Five (10.4%) stillborn infants weighed < 10(th) centile at delivery (adjusted odds ratio (aOR), 2.70 (95% CI, 1.06-6.92)); 23 (47.9%) cases of stillbirth were considered unexplained. Pre-eclampsia was associated with stillbirth (odds ratio, 4.46 (95% CI, 1.99-9.96)) but no other antenatal factors, including ultrasound measures of fetal growth, showed a significant association with this outcome. Pre-eclampsia constituted 9.6% of the population-attributable fraction for stillbirth. Severe composite adverse outcome was associated only with pre-existing diabetes (aOR, 2.82 (95% CI, 1.02-7.85)) and nulliparity (aOR, 1.56 (95% CI, 1.19-2.04)). Conclusions The potential to predict mortality and severe morbidity in fetuses without ultrasound evidence of SGA and FGR is poor. In these fetuses, the role of ultrasound in further reducing adverse outcomes at term is limited. (c) 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.