Mortality in multiple vs. singleton very low birth weight infants in GermanyA population-based study

INTRODUCTION: In several large cohorts from the United States and China, multiple as opposed to singleton birth was found to be associated with increased mortality, while studies from European countries have yielded conflicting results. We aimed to assess the association between plurality and survival of very low birth weight infants in relation to gestational age. METHODS: Data of preterm infants <1500g birth weight obtained from annually published quality improvement data mandatorily collected from all hospitals in Germany (2010-2017, 2019-2024) were analyzed for mortality of singletons versus multiples. RESULTS: Among infants below 1500g birth weight (n=128,057), twins and higher-order multiples accounted for 28.2% and 3.9%, as opposed to 3.5% and 0.1% in all neonates (n=9,986,821). Mortality prior to discharge was lower in twins (7.3%) and triplets (6.2%) than in singletons (9.0%) [relative risk (RR) 0.811, 95% confidence interval (CI) 0.777-0.846, and 0.689 (0.618-0.769), respectively]. However, in infants below 25 weeks' gestation, mortality was higher in multiples (40.5%) than in singletons (37.6%) [RR (95% CI) 1.076 (1.031-1.124)], whereas it was lower in multiples than in singletons infants with a gestational age of 25-27 weeks (8.5% vs 9.4%, RR (95% CI) 0.907 (0.837-0.983)), 28-30 weeks (2.1% vs 2.9%, RR (95% CI) 0.737 (0.650-0.835)) and more than 30 weeks (1.2% vs 2.0%, RR (95% CI) 0.583 (0.484-0.703)). CONCLUSIONS: In this large population-based cohort of preterm infants below 1500g birth weight, multiples had higher survival rates than singletons, except those born before 25 weeks' gestation.