Long-term Trends and Influencing Factors of Low Birth Weight in Hainan Island, China's Largest Free Trade Zone: A Retrospective Study from 2010 to 2021

Background Low birth weight (LBW) poses substantial health risks for neonates and can have enduring consequences, such as higher healthcare costs and adverse effects on human capital and productivity. However, comprehensive epidemiological data on LBW in Hainan Province, China's Largest Free Trade Port and a strategically vital tropical region, remain strikingly limited. This study aims to assess the incidence of LBW in Hainan Free Trade Port and identify contributing risk factors. Methods This population-based retrospective cohort study analyzed 1,538,023 live births in Hainan Province from 2010 to 2021. Data on neonatal and parental demographics, clinical factors, and socioeconomic indicators were systematically collected. LBW, VLBW, and ELBW were classified based on birth weight. Spatial analysis used ArcGIS to assess geographic distribution. Temporal trends were analyzed via joinpoint regression. Multivariate binary logistic regression identified risk factors for LBW. Results The overall LBW incidence was 5.96%, with VLBW at 0.29% and ELBW at 0.02%. Joinpoint regression identified distinct temporal patterns; although the LBW rate remained stable from 2010–2015 (APC: -0.7209; 95% CI: -2.4331–1.0214; P  = 0.3582), it increased significantly from 2015–2021(APC: 1.9190; 95% CI: 0.5875–3.2682; P  = 0.0112). In contrast, both VLBW and ELBW showed sustained upward trends throughout the study period (APC = AAPC: 8.2298, 20.7718; 95% CI: 7.0264–9.4468, 15.1269–26.6934; both P  < 0.0001). The geospatial analysis identified regional heterogeneity, with Wuzhishan exhibiting the highest LBW incidence (7.41%), and Haikou showing peak rates of VLBW (0.55%) and ELBW (0.06%). The occurrence of LBW, VLBW, and ELBW in Hainan Province was distributed in a follow-up manner. Multivariate binary logistic regression analysis demonstrated that parental age (< 20 or > 35 years), minority ethnicity, preterm birth, multiple pregnancies, and delivery to a tertiary hospital were significantly associated with a higher risk of LBW. Conversely, male sex, post-term gestation, urban residency, higher regional GDP per capita, and a higher density of healthcare workers demonstrated significant protective effects against LBW. Conclusion There's a significant increase in LBW - related incidences in Hainan. Targeted prevention for high - risk groups is needed.