Fetal Growth Restriction at a Universal Late Third‐Trimester Scan and Relationship With Adverse Outcome: Retrospective Cohort Study

Objective To examine the contribution of fetal growth restriction ultrasound phenotypes to adverse perinatal outcomes at term. Design Retrospective population‐based cohort study. Setting John Radcliffe Hospital, Oxford, UK where universal ultrasound at 35 +1 –36 +6 weeks is performed. Population Congenital abnormalities and births before the scan were excluded. Singleton foetuses were categorised as five mutually exclusive phenotypes using a hierarchical approach: ISUOG fetal growth restriction (FGR), according to Delphi criteria; Constitutional small‐for‐gestational‐age (SGA) (estimated fetal weight [EFW] < 10th centile); Appropriate‐for‐gestational‐age (AGA) with either cerebroplacental ratio < 5th centile or umbilical artery >95th centile; AGA with slowing abdominal circumference growth velocity (ACGV < 10th centile); Normal AGA; Methods Univariate logistic regression was employed using normal AGA as the reference group to estimate odds ratio with 95% confidence intervals. Group differences for continuous variables were assessed using mean differences with confidence intervals through a generalised linear model. Main Outcome Measures Stillbirth (SB); composite adverse outcome (CAO) (1+ of Grade 2–3 encephalopathy, cooling, ventilation > 24 h, or perinatal death); severe SGA at birth; neonatal unit admission; obstetric interventions. Results Among 45 179 pregnancies, 54 SBs (0.1%) and 253 CAOs (0.6%) occurred. Normal AGA foetuses at the 35 +1 –36 +6 week scan accounted for 82% of all pregnancies and for 43 (79.6%) SBs and 205 (81%) with the CAO, yet only 37.3% of neonates born with severe SGA. The absolute risk of SB and CAO was similar in all groups (0.1%–0.2%). Conclusions Term FGR and ‘normal’ babies have similar perinatal risks, presumably because of intervention. Despite a detection rate of 62.7% for severe SGA, most adverse outcomes occurred in pregnancies with a normal scan.