Admission temperature in very preterm infants 2012-2021: a Nationwide Quality Registry Study, Norway.

Objective: To examine the distribution and time trends of admission temperature in very preterm infants, effects of temperature-preserving interventions and associations between hypothermia and outcomes.

Methods: Population-based cohort study of infants <32 gestational weeks without lethal malformations admitted to a neonatal intensive care unit within 2 hours of birth between 1 January 2012 and 31 December 2021. Hypothermia was defined as mild (36.0°C-36.4°C), moderate (34.5°C-35.9°C) or severe (<34.5°C). Associations between admission temperature and outcomes were investigated using multivariate logistic regression, adjusting for sex, weight Z-score, gestational age, antenatal steroids, surfactant and hospital.

Results: In total, 2457/4879 (50.4%) had normal admission temperatures between 36.5°C and 37.5℃, 1314 (26.9%) had mild hypothermia and 886 (18.2%) had moderate to severe hypothermia, with a significant interhospital variance of 7%-40%. Moderate to severe hypothermia decreased from 24% in 2012 to 16% in 2021 (p_trend<0.001). Measuring temperature before leaving the delivery unit correlated with lower incidence of moderate to severe hypothermia (42% vs 58%, p<0.001). Admission temperature was inversely associated with mortality (adjusted OR 1.5, 95% CI 1.1 to 2.0 for moderate and 2.4, 95% CI 1.1 to 4.9 for severe hypothermia) and with surgical necrotising enterocolitis or intestinal perforation (adjusted OR 1.7, 95% CI 1.1 to 2.7 for moderate and 3.1, 95% CI 1.3 to 7.7 for severe hypothermia).

Conclusions: Although the incidence of hypothermia decreased during the study period, it remains a concern due to significant associations with adverse outcomes. Areas for further improvement include addressing interhospital variance and enhancing temperature monitoring in the delivery unit.