Study main groups.

BackgroundAutonomic nervous system (ANS) maturation is crucial for neonatal adaptation, but in preterm infants, this process is often delayed, leading to increased vulnerability. Heart rate variability (HRV) provides a non-invasive measure of ANS function, yet existing evidence is contradictory regarding how birth gestational age influences HRV development at comparable postmenstrual ages.ObjectiveThis study aims to investigate HRV metrics at 35–36 weeks postmenstrual age in preterm neonates with a wide range of birth gestational ages. We hypothesize that lower birth gestational age correlates with reduced HRV, indicating delayed ANS maturation and diminished parasympathetic tone.MethodsWe conducted a longitudinal cohort study of preterm neonates divided into two groups: Group A (28–33 weeks GA) and Group B (34–36 weeks GA). Short-term HRV recordings (mean duration 17 minutes, SD 4.3) were obtained within 24 hours after birth, on the 3rd–4th postnatal day, and again at 35–36 weeks PMA for neonates born before 35 weeks. HRV features included time-domain, frequency-domain, and non-linear measures.ResultsOf 132 recruited preterm neonates, 88 were included in the final analysis. Preterm neonates with higher gestational age at birth (Group B) exhibited elevated time-domain measures (HTI, SDNN, RMSSD, pNN50) and higher frequency-domain indices (LF, LF/HF, TP) compared with those born earlier (Group A). Compared with Group B, Group A (28–33 weeks GA) had higher mean heart rates and exhibited stronger long-range correlations in heart rate dynamics.ConclusionThis study demonstrates that advancing gestational age is associated with greater parasympathetic modulation and more balanced sympathovagal control. Birth gestational age is a strong determinant of autonomic nervous system development at 35–36 weeks postmenstrual age. These findings highlight the importance of stratifying by gestational age in HRV studies and may inform neurodevelopmental monitoring and NICU care strategies.背景：自主神经系统（Autonomic nervous system, ANS）成熟对新生儿适应具有关键意义，但早产儿的该成熟过程往往延迟，使其易感性显著升高。心率变异性（Heart rate variability, HRV）是评估自主神经系统功能的无创手段，但现有研究关于出生胎龄如何对同等月经后胎龄（postmenstrual age, PMA）下的心率变异性发育产生影响的结论尚存矛盾。 研究目的：本研究旨在探究出生胎龄跨度较大的早产儿在月经后胎龄35~36周时的心率变异性指标。本研究提出假说：更低的出生胎龄与降低的心率变异性存在相关性，提示自主神经系统成熟延迟以及副交感神经张力减弱。 研究方法：本研究针对早产儿开展一项纵向队列研究，将受试者分为两组：A组（出生胎龄28~33周）与B组（出生胎龄34~36周）。对于出生胎龄不足35周的早产儿，分别于出生后24小时内、出生后第3~4天，以及月经后胎龄35~36周时采集短时程心率变异性记录（平均时长17分钟，标准差4.3）。心率变异性分析指标涵盖时域、频域及非线性分析方法。 研究结果：本研究共招募132名早产儿，最终88名纳入最终分析。与出生胎龄更低的A组相比，B组早产儿的时域指标（HTI、SDNN、RMSSD、pNN50）及频域指数（LF、LF/HF、TP）均显著升高。与B组相比，A组（28~33周GA）的平均心率更高，且心率动力学表现出更强的长程相关性。 研究结论：本研究证实，出生胎龄越高，早产儿的副交感神经调节作用越强，交感-迷走神经调控也更为平衡。出生胎龄是早产儿在月经后胎龄35~36周时自主神经系统发育的重要决定因素。上述研究结果凸显了在心率变异性研究中按胎龄分层的重要性，或可为神经发育监测及新生儿重症监护病房（Neonatal Intensive Care Unit, NICU）的护理策略提供参考。