The Neonatal Line in Primary Teeth: A Systematic Review and Meta-analysis of Its Forensic, Clinical, Anthropological, and Archaeological Applications

The neonatal line (NNL) is an accentuated histological feature of dental enamel formed around the time of birth. It provides a permanent marker of parturition and has been linked to maternal, perinatal, and neonatal conditions. While its significance has been explored in forensic, clinical, anthropological, and archaeological contexts, existing reviews have remained descriptive, and no quantitative synthesis has been performed to date. To systematically review and meta-analyse quantitative evidence on neonatal line width, examining its associations with maternal and perinatal factors, and evaluating its translational relevance across multiple disciplines. This review was prospectively registered in PROSPERO (CRD420251080118) and conducted in accordance with PRISMA 2020 guidelines. Eligible studies included clinical, forensic, anthropological, and archaeological investigations reporting quantitative measurements of NNL width. Databases searched were PubMed, Scopus, Scholar and Web of Science, supplemented by manual reference screening. Risk of bias was assessed using the Joanna Briggs Institute (JBI) critical appraisal tools. A random-effects meta-analysis was performed to estimate pooled mean NNL width and to evaluate subgroup contrasts (delivery mode, gestational length). Fourteen studies (n = 883 teeth) met inclusion criteria. The pooled mean NNL width was 10.83 µm (95% CI 9.31–12.34), with substantial heterogeneity (I² = 97.2%). Vaginal delivery was associated with significantly wider NNLs compared to Caesarean section (+4.14 µm, 95% CI +1.99 to +6.28). Preterm birth was similarly linked to wider NNLs than term birth (+4.40 µm, 95% CI +1.98 to +6.82). Individual studies reported associations between wider NNLs and maternal hypertension, diabetes, depression, and occasional alcohol use, while narrower lines were observed in children with obesity or cerebral palsy. Archaeological populations showed somewhat wider NNLs compared to modern cohorts. Risk of bias was generally moderate, with strongest evidence from large prospective cohorts. The neonatal line is a measurable and consistent marker of perinatal stress, with width reflecting maternal health, delivery conditions, and neonatal outcomes. This first quantitative synthesis confirms its translational relevance in forensic identification, clinical research, and bioarchaeological reconstruction. Future studies should adopt standardized measurement protocols, larger cohorts, and multivariate analyses to strengthen the evidence base. Quantitative assessment of the neonatal line can provide a translational biomarker linking perinatal health, developmental stress, and enamel formation. Standardized NNL measurement protocols could enhance diagnostic precision in pediatric, forensic, and anthropological contexts. • First meta-analysis of neonatal line (NNL) width across 14 studies • Vaginal delivery and preterm birth associated with wider NNLs • Maternal hypertension, diabetes, and depression linked to increased width • NNL absent in stillbirths, supporting its forensic diagnostic value • Translational significance spans clinical, forensic, anthropological, and archaeological fields