Single versus longitudinal scans in the third trimester: a multicenter randomized clinical trial on screening for late-onset intrauterine fetal growth restriction (The RCT on Evaluation of LAte Iugr Screening study)

Background: Undiagnosed fetal smallness is strongly associated with adverse perinatal outcomes. Despite robust evidence that late third trimester ultrasound improves small for gestational age detection, the question of whether routine ultrasound assessment in late pregnancy can improve perinatal outcome remains unresolved. Objective: The objective of the study was to assess whether the addition of a 35 to 37-week scan in low-risk pregnancy would improve the detection of small for gestational age at birth without increasing cesarean section rates or neonatal morbidity. Study design: Open label multicentric randomized trial recruiting nulliparous low-risk pregnant women in 10 Italian centers between January 2021 and March 2023. Patients were randomly assigned at mid-trimester scan to either routine care (single scan at 28-32 weeks) or intervention (routine care plus additional scan at 35-37 weeks). The primary endpoint was prenatal detection of small for gestational age neonate with birthweight <10th centile. Predefined secondary outcomes included detection of severe fetal smallness defined as birthweight