Background Birth weight (BW) Z-score is associated with outcomes in very preterm infants (VPIs). This study aimed to investigate the association between BW Z-score and the adverse outcomes in VPIs. Methods This retrospective cohort study included VPIs admitted to a tertiary neonatal intensive care unit between 1 January 2014 and 31 December 2023. Restricted cubic splines and multivariable logistic regression models were employed to assess associations between BW Z-score and primary outcomes. Infants were categorised based on the identified turning point of Z=−0.35 in the Z-score distribution, where the risk gradient changed most sharply. The primary outcome was bronchopulmonary dysplasia (BPD) or mortality at 36 weeks postmenstrual age or discharge. Results Among 4632 included VPIs, a turning point at Z=−0.35 was identified. Compared with those with Z≥−0.35, VPIs with Z<−1 exhibited higher risks of primary outcomes (OR 3.10, 95% CI 2.53 to 3.79), while those with BW Z-score between −1 and −0.35 also showed increased risks (OR 1.81, 95% CI 1.52 to 2.15). Subgroup and sensitivity analyses further supported the robustness of these findings. Conclusion Compared with BW Z-score above −0.35, both substantially negative BW Z-score<−1 and moderate lower BW Z-score between −1 and −0.35 are associated with increased risk of BPD and mortality in VPIs. The findings underscore the importance of considering BW Z-score as a continuous variable in risk stratification and management of VPIs.
Liu et al. (Thu,) studied this question.