Autonomic nervous system maturation in the premature extrauterine milieu.

In premature infants, we investigated whether the duration of extrauterine development influenced autonomic nervous system (ANS) maturation. We performed a longitudinal cohort study of ANS maturation in preterm infants. Eligibility included birth gestational age (GA) < 37 weeks, NICU admission, and expected survival. The cohort was divided into three birth GA groups: Group 1 (≤29 weeks), Group 2 (30–33 weeks), and Group 3 (≥34 weeks). ECG data were recorded weekly and analyzed for sympathetic and parasympathetic tone using heart rate variability (HRV). Quantile regression modeled the slope of ANS maturation among the groups by postnatal age to term-equivalent age (TEA) (≥37 weeks). One hundred infants, median (Q1−Q3) birth GA of 31.9 (28.7–33.9) weeks, were enrolled: Group 1 (n = 35); Group 2 (n = 40); and Group 3 (n = 25). Earlier birth GA was associated with lower sympathetic and parasympathetic tone. However, the rate of autonomic maturation was similar, and at TEA there was no difference in HRV metrics across the three groups. The majority of infants (91%) did not experience significant neonatal morbidities. Premature infants with low prematurity-related systemic morbidity have maturational trajectories of ANS development that are comparable across a wide range of ex-utero durations regardless of birth GA.