Assessment of the fetal Evans Index in pregnancies complicated by fetal growth restriction

Fetal growth restriction (FGR) can affect fetal brain development despite adaptive circulatory redistribution. The fetal Evans Index (EI)-the ratio of frontal horn width to inner cranial diameter-may capture proportional cranial remodeling in FGR.

In a prospective case-control study of singleton pregnancies ≥32 weeks, FGR was defined by Delphi consensus criteria. EI and frontal proportional ratios were obtained on the standardized axial transventricular plane. We evaluated how well EI distinguished FGR cases from controls and whether its association with NICU admission was independent of conventional fetal growth measurements.

The cohort comprised 129 pregnancies (67 FGR, 62 controls). EI was lower in FGR than in controls (0.28 ± 0.02 vs 0.30 ± 0.02; p < 0.001), alongside reduced frontal horn width and a lower FABD/OFD ratio (p < 0.001). EI correlated strongly with frontal horn width (r = 0.752, p < 0.001). EI provided moderate discrimination for FGR (AUC = 0.707, 95% CI 0.617-0.797; cut-off 0.297; sensitivity 78.8%, specificity 51.6%). NICU admission was markedly higher in FGR (44.8% vs 4.8%; p < 0.001). EI ≥ 0.297 was associated with reduced NICU odds in univariate analysis (OR = 0.20, 95% CI 0.07-0.62), but not after adjustment (adjusted OR = 0.38, 95% CI 0.11-1.38); abdominal circumference percentile remained independently associated with NICU admission (adjusted OR = 0.97, 95% CI 0.95-0.99).

Late-onset FGR is associated with reduced EI and altered frontal proportional indices, suggesting subtle anterior cerebral remodeling rather than ventriculomegaly. EI may provide complementary neurosonographic information, but its stand-alone diagnostic or prognostic value appears limited.