Hypothermia is associated with elevated mortality in the preterm infant. The preterm infant's thermoregulatory capacity is limited, and the thermal environment in an incubator is often perturbed by nursing procedures. We evaluated the incidence of a postnatal low body temperature and hypothermia in preterm infants and its association with mortality.

We measured the lowest body temperature during the first 24h of life (T_{Body Nadir 24h}) and hypothermia (T_{Body Nadir 24h}<36.0°C) in preterm infants (gestational age: 23⁰–31⁶ weeks) in a neonatal intensive care unit. Prenatal and neonatal characteristics associated with mortality were identified in univariate and multivariable analyses.

A total of 102 preterm infants were included, with a mean gestational age at birth of 28.4±2.3 weeks. The incidence of hypothermia during the first 24h was 53%. A Cox multivariate regression model indicated that T_{Body Nadir 24h} (hazard ratio (HR) [95% confidence interval]: 0.57 [0.36–0.90]; P=0.017), gestational age (0.62 [0.50–0.76]; P<0.001), and amine use (4.55 [2.01–10.28]; P=0.001) were significantly associated with mortality. When considering a threshold for T_{Body Nadir 24h}, a value of 35.0°C had the highest HR (3.30 [1.42–7.68]; P<0.01).

In preterm infants, the incidence of hypothermia during the first 24h of life was 53%. T_{Body Nadir 24h} had an influence on mortality, independently of other factors (notably birth weight and amine use). Within the framework of a quality improvement strategy, the implementation of a thermoregulation bundle is required to prevent hypothermia and decrease mortality in preterm infants.