Umbilical coiling index: Revisiting an underutilized perinatal risk marker

Umbilical cord coiling, a physiological adaptation that safeguards fetal blood flow, has drawn renewed attention as a potential marker of perinatal risk. This review re-examines evidence from 1994 to 2025 on the Umbilical Coiling Index (UCI) and its association with adverse obstetric outcomes. A systematic search was performed across PubMed, Scopus, Cochrane, and Embase in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses 2020 guidelines. From 2356 retrieved records, 42 studies met the inclusion criteria after full-text screening, and 21 high-quality publications were retained for detailed synthesis and citation. Eligible reports encompassed observational, cohort, and meta-analytic investigations evaluating abnormal coiling and perinatal endpoints. Across meta-analyses and pooled estimates, abnormal UCI – whether hypocoiling or hypercoiling – was consistently linked to preterm birth, fetal growth restriction, low Apgar scores, and stillbirth, with odds ratios typically ranging from 1.5 to 2.3. Heterogeneity among studies reflected differences in gestational age, measurement technique, and population context. Despite these variations, the direction of association remained uniform, supporting the clinical relevance of UCI as an early structural biomarker. The principal limitations include non-standardized definitions and interobserver variability. Emerging evidence suggests that integration with Doppler velocimetry and artificial intelligence-assisted imaging could enhance diagnostic precision, particularly in low-resource settings. UCI assessment thus holds promise as a complementary screening parameter warranting multicenter validation and methodological standardization before clinical implementation.