Coronal Subarachnoid-Space Measurements in Fetuses with Growth Restriction and Appropriate-for-Gestational-Age Controls: A Prospective Comparative Study.

OBJECTIVES: To compare coronal sinocortical width (SCW) and craniocortical width (CCW) between fetuses with fetal growth restriction (FGR) and appropriate-for-gestational-age (AGA) fetuses and to assess interobserver agreement. METHODS: This prospective cross-sectional comparative study included 281 singleton pregnancies examined at 28 + 0 to 36 + 6 weeks: 145 with FGR and 136 AGA controls. Two observers independently measured SCW and CCW transabdominally in a standardized coronal plane. Primary analyses used gestational-age-adjusted linear regression with Holm correction. Head-circumference sensitivity analyses and interobserver agreement assessments were performed. RESULTS: Mean SCW was 2.26 ± 0.86 mm in the FGR group and 2.68 ± 0.96 mm in the AGA group; the adjusted difference was -0.426 mm (95% CI, -0.642 to -0.210; Holm-adjusted p < .001). For CCW, the FGR-by-gestational-age-window interaction was significant (p = .006), with a larger adjusted difference at 28 + 0 to 30 + 6 weeks (-0.707 mm; Holm-adjusted p = .007) and no significant differences in the later windows after Holm correction. Single-measure absolute-agreement ICCs were 0.869 for SCW (95% CI, 0.726-0.967) and 0.863 for CCW (95% CI, 0.813-0.904); corresponding average-measures ICCs were 0.930 (95% CI, 0.841-0.983) and 0.926 (95% CI, 0.897-0.949), respectively. CONCLUSIONS: Coronal SCW was smaller, on average, in fetuses with FGR, whereas CCW differences varied across gestational-age windows. After head-circumference adjustment, the SCW difference persisted, whereas the CCW estimate was attenuated and no longer statistically significant. The Bland-Altman limits of agreement exceeded the average between-group differences, limiting individual-level interpretation. Further longitudinal studies are needed to determine clinical relevance.