Association of Birthweight Discordance with Adverse Birth Outcomes Among Live-Born Twins: A Multi-Center Study in China

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Abstract
Twin pregnancies, accounting for a rising proportion of births globally, present significant public health challenges in China. Birthweight discordance (BWD), a critical complication, remains understudied in its epidemiological context, particularly regarding its population-level associations with adverse neonatal outcomes. This multi-center, retrospective cohort study leveraged data from 21 hospitals across 18 Chinese cities (2018–2020) to assess BWD and its epidemiological implications. Ordinal logistic regression with random effects was used to explore their association. BWD was defined as: [(larger birthweight − smaller birthweight) / larger birthweight] × 100% and categorized into four grades: I (≤15%), II (>15% to 20%), III (>20% to 25%), and IV (>25%). Among 6437 twin pairs, 73.6% were classified as Grade I (no BWD), while 10.7%, 7.1%, and 8.6% constituted Grades II, III, and IV discordance, respectively. Dose-response relationships emerged: each incremental BWD elevated risks of small vulnerable newborns (aOR = 1.83, 95% CI 1.76–1.90), small for gestational age (aOR = 1.23, 95% CI 1.18–1.29), low birthweight (LBW, aOR = 1.16, 95% CI 1.13–1.20), very LBW (aOR = 1.63, 95% CI 1.53–1.73) and extreme LBW (aOR = 1.82, 95% CI 1.61–2.05). Smaller twins exhibited disproportionately higher adverse outcome rates than larger twins. Sensitivity analyses confirmed robustness across specific subgroups. BWD exceeding 20% affects 15.7% of live-born twins in China, mirroring rates in high-income settings. BWD demonstrates strong dose-response relationships with adverse outcomes, validating its utility for twin health stratification. These findings call for integrating BWD assessment into prenatal surveillance and risk-adapted care to reduce neonatal morbidity/mortality, urging clinicians and policymakers to prioritize perinatal outcome equity.

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