OC14.03: Single scan screening versus longitudinal scan screening of fetal growth restriction in the third trimester: multicentre randomised protocol (RELAIS)

Universal third trimester screening for fetal growth anomalies is not yet recommended by international guidelines because of lack of evidence of benefit. The consequence is that intrauterine fetal growth restriction is still mostly unpredicted leading to unchanged adverse perinatal outcomes for these pregnancies. Open label multicentric randomised trial recruiting nulliparous singleton pregnancies with no risk factors for FGR in 10 different Italian tertiary care centres. Women were randomly assigned at the time of the midtrimester scan to either the Single Scan Protocol (28-32 weeks) or to the longitudinal scan protocol (scan both at 28-32 AND 35-37 weeks). This study was designed to generate level 1 evidence of diagnostic effectiveness with the main outcome being the performance of the two protocols in identifying late preterm and term FGR fetuses. 790 patients were eligible for the analysis (396 in the single scan protocol and 394 in the longitudinal scan protocol). The latter identified 19 FGR fetuses according to the Delphi criteria (4.8%) versus 10 (2.5%) in the Single Scan group (OR 1.96 [95% CI 0.90–4.26]; p < 0.001). There was a significant increase in detection of SGA with the additional scan at 35-37 weeks compared to the single scan at 28-32 weeks (OR 3.29 [95% CI 1.39–7.78]; p = 0.026). Neonatal admission in NICU was significantly lower in the longitudinal scan group (OR 0.27 [95% CI 0.09–0.8]; p < 0.001). Comparing the SGA detection rates at the 28-32 weeks and 35-37 weeks scans we found that the additional 35-37 weeks scan detects 10x more SGA (18.4% vs 1.5%) with a significant association (OR = 11.85 [95% CI 3.75; 37.48]). Universal late third trimester increases the detection of late FGR and reduces the rate of neonatal admission to NICU. Implementation of routine third trimester ultrasound at 35-37 weeks' gestation in a low-risk population is justifiable on the basis of improved FGR/SGA detection resulting in improved perinatal outcomes.