Abstract:

Objective To explore the risk factors of early postnatal hypothermia in premature infants and whether the rewarming rate after the implementation of standard rewarming measures is a key factor affecting early clinical outcomes. Methods This study was a retrospective cohort study, selecting the clinical data of premature infants in the region who were treated by the hospital's neonatal transfer team from January 2022 to December 2024. According to the body temperature before transfer, they were divided into the normal body temperature group (≥36.5 ℃) and the hypothermia group (<36.5 ℃). The hypothermia group was given a unified rewarming strategy. According to the rewarming rate after insulation intervention, the hypothermia group was further divided into the slow rewarming group (<0.5 ℃/h) and the rapid rewarming group (≥0.5 ℃/h). Clinical outcomes within the first 7 days after birth (including mortality, pulmonary hemorrhage, severe intracranial hemorrhage, coagulation abnormalities, and the proportion requiring one or more vasoactive agents) and the proportion of infants still requiring invasive mechanical ventilation beyond 7 days were compared across different gestational age subgroups (<32⁺⁰ weeks and 32⁺⁰-36⁺⁶ weeks). Results A total of 1,016 preterm infants from 6 delivery institutions were included. Among the 250 infants with a gestational age of <32⁺⁰ weeks, 214 developed hypothermia (85.6%); among the 766 infants with a gestational age of 32⁺⁰-36⁺⁶ weeks, 530 developed hypothermia (69.2%). The incidence of hypothermia was significantly higher in the <32⁺⁰ weeks group compared to the 32⁺⁰-36⁺⁶ weeks group (P<0.001). The normal temperature group comprised 272 cases (26.8%), while the hypothermia group included 744 cases (73.2%). Within the hypothermia group, 338 cases were in the slow rewarming group and 406 in the rapid rewarming group. Among preterm infants with a gestational age of <32⁺⁰ weeks, compared with the normal body temperature group, the mothers in the hypothermia group were older, the gestational age of preterm infants at birth was smaller, the birth weight was lower, and the weight-for-gestational-age Z-score was lower. The differences were all statistically significant (P<0.05). Among preterm infants with gestational ages ranging from 32⁺⁰ to 36⁺⁶ weeks, the preterm infants in the hypothermia group had a lower birth weight (P<0.05) and a higher proportion of intubation in the delivery room (P<0.014). Further comparison was made between the slow rewarming group and the rapid rewarming group. Among preterm infants with a gestational age of <32⁺⁰ weeks, the proportion of assisted reproduction was lower and the proportion of males was higher in the slow rewarming group, and the differences were statistically significant (P<0.05). Among preterm infants with gestational ages ranging from 32⁺⁰ to 36⁺⁶ weeks, the slow rewarming group had a smaller gestational age at birth (P<0.05). In preterm infants with a gestational age of <32⁺⁰ weeks, the proportions of infants still requiring invasive mechanical ventilation beyond 7 days were higher in both the slow and rapid rewarming groups compared to the normal temperature group (P<0.014). Among preterm infants with a gestational age of 32⁺⁰ to 36⁺⁶ weeks, no significant differences in short-term outcome indicators were observed between the hypothermia group and the normal body temperature group. Among all preterm infants of gestational age, no significant differences were observed in the short-term clinical outcome indicators between the slow rewarming group and the rapid rewarming group. Conclusions The incidence of early hypothermia in preterm infants within the region is relatively high. Hypothermia in preterm infants with a gestational age of <32⁺⁰ weeks increases the probability of requiring invasive respiratory support 7 days after birth. It is particularly important to emphasize the prevention of hypothermia in extremely preterm infants immediately after birth in the delivery room. Under standard rewarming measures, the speed at which preterm infants' body temperature rises does not have a significant impact on their early clinical outcomes after birth.

Key words: preterm infant transport, hypothermia, rewarming rate