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

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. 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(i.e., 2499 g or below), very low birth weight(VLBW, < 1500 g), and extremely low birth weight (ELBW, < 1000 g) were classified based on birth weight. Spatial analysis used ArcGIS to assess geographic distribution. Temporal trends in LBW, VLBW, and ELBW incidence were analyzed using joinpoint regression, with segment-specific annual percentage changes (APC) and overall average annual percentage changes (AAPC) estimated over the full study period. Categorical variables were presented as frequencies and percentages, and between-group differences in the incidence of LBW were assessed using the χ² test.Multivariate binary logistic regression identified risk factors for LBW. 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 to 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%). Multivariate binary logistic regression analysis demonstrated that parental age (Maternal age < 20 or ≥ 35 years; Paternal age < 22 or ≥ 40), minority ethnicity, preterm birth, and multiple pregnancies were significantly associated with a higher risk of LBW. Conversely, male sex, post-term gestation, urbanresidency, and higher regional GDP per capita, demonstrated significant protective effects against LBW. The incidence of LBW in Hainan increased significantly after 2015, accompanied by sustained upward trends in VLBW and ELBW throughout the study period. Targeted prevention strategies focusing on modifiable risk factors and high-burden regions are urgently needed.