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

Background: 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.

Methods: 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: [( - ) / ] × 100% and categorized into four grades: I (≤15%), II (>15% to 20%), III (>20% to 25%), and IV (>25%).

Results: 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 (a = 1.83, 95% CI 1.76-1.90), small for gestational age (a = 1.23, 95% CI 1.18-1.29), low birthweight (LBW, a = 1.16, 95% CI 1.13-1.20), very LBW (a = 1.63, 95% CI 1.53-1.73) and extreme LBW (a = 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.

Conclusion: 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.