*2.5. Group Stratification*

In a first step, the neonates were stratified into term neonates (≥37<sup>+</sup><sup>0</sup> weeks of gestation) and preterm neonates (<37<sup>+</sup><sup>0</sup> weeks of gestation). In a second step, sub-groups for preterm neonates were generated: (i) extremely preterm infants (EPI) born ≤28<sup>+</sup><sup>0</sup> weeks of gestation, (ii) very preterm infants (VPI) born between >28<sup>+</sup><sup>0</sup> and <32<sup>+</sup><sup>0</sup> weeks of gestation, and (iii) late preterm infants (LPI) born between ≥32<sup>+</sup><sup>0</sup> and <37<sup>+</sup><sup>0</sup> weeks of gestation. According to the WHO, body temperature stages were defined as follows: hyperthermia (>37.5 ◦C), normothermia (36.5–37.5 ◦C), mild hypothermia (36.0–36.4 ◦C), moderate hypothermia (32.0–35.9 ◦C), and severe hypothermia (<32.0 ◦C) [1].
