The Heart’s Hidden Record: What HRV Reveals Years After Preterm and Low-Birth-Weight Births

Every heartbeat carries a hidden signature. Even when your pulse looks perfectly steady on a monitor, the intervals between individual beats fluctuate by milliseconds from one moment to the next, and that fluctuation, known as heart rate variability, or HRV, is one of the most sensitive windows scientists have into the autonomic nervous system. A new systematic review and meta-analysis published in Pediatric Research by Lisa Gistelinck of KU Leuven and colleagues has now asked a deceptively simple question: does that signature look different in people who were born preterm, small for gestational age, or with low birth weight, once they leave the neonatal intensive care unit and go home? The answer, drawn from 156 effect sizes across 27 studies spanning infancy to adulthood, is more nuanced than either alarmists or skeptics might expect.

The stakes are far from academic. Perinatal risk factors such as preterm birth, intrauterine growth restriction, and low birth weight affect a substantial share of all births worldwide, and decades of epidemiological work have linked them to elevated risks of hypertension, ischemic heart disease, heart failure, type 1 and type 2 diabetes, obesity, and neurodevelopmental difficulties later in life. Large cohort studies, including national registries from Scandinavia, have shown that people born preterm carry measurably higher odds of cardiovascular disease well into middle age. If HRV could serve as an early, noninvasive marker of the autonomic consequences of an adverse perinatal start, clinicians might one day identify which NICU graduates need closer cardiovascular surveillance decades before symptoms appear.

HRV is not a single number but a family of metrics. Time-domain measures quantify the statistical spread of beat-to-beat intervals over a recording, while frequency-domain methods decompose those fluctuations into bands that roughly reflect sympathetic and parasympathetic, or vagal, contributions. Vagal tone, in particular, has fascinated researchers because it tracks not only cardiac health but also self-regulation, attention, and social engagement, themes explored in frameworks such as polyvagal theory. In newborns, HRV matures rapidly, and disruptions during the NICU period, from procedural pain to prolonged hospital stays and surgery, are well documented. What remained murky was what happens after discharge, when the monitors come off and the child, adolescent, or adult lives in the ordinary world.

To bring order to that murkiness, the Leuven team searched PubMed, EMBASE, Web of Science, Scopus, and APA PsycArticles through April 2025, supplemented by ClinicalTrials.gov and backward reference screening. They included peer-reviewed studies that compared HRV between perinatal risk populations and healthy full-term controls after hospital discharge, ultimately extracting 156 effect sizes from 27 studies. The scale matters: this is the first meta-analysis to quantify HRV differences across perinatal risk groups from infancy all the way to adulthood, focusing specifically on the post-discharge window that most families actually inhabit.

The headline result is a shrug with a twist. Across all studies, the pooled effect was small and statistically non-significant, a standardized mean difference of d equal to minus 0.21 with a p-value of 0.14, and the heterogeneity between studies was enormous, with an I-squared of 89.3 percent. In plain language, on average, perinatal risk populations did not show reliably lower HRV than controls, and the individual studies disagreed so wildly that any single pooled number is almost meaningless. For a field that has produced dozens of seemingly contradictory papers, this is both a humbling verdict and a clarifying one: the inconsistency is not noise to be wished away but a signal about where and when to look.

That signal becomes visible when the data are sliced by condition. The most consistent HRV reductions appeared in growth-related risk groups, namely children and infants who were born small for gestational age or with intrauterine growth restriction. This makes physiological sense. Fetal growth restriction typically reflects chronic compromise of the placental blood supply, a stressor that can reshape cardiovascular regulation before the first breath. Studies of growth-restricted children, from recordings during sleep and wake stages to antenatal hemodynamic findings tracked into school age, repeatedly found blunted variability, suggesting that the autonomic imprint of restricted growth persists well beyond the neonatal period.

Preterm birth and low birth weight told a different story. Neither showed a significant overall effect, yet both displayed substantial between-study heterogeneity across age groups, hinting that timing is everything. The meta-analysis found that younger samples showed larger group differences than older samples, with pronounced HRV alterations in preterm-born infants that shrank and became more variable in older children, adolescents, and adults. One provocative thread in the underlying literature is the possibility of premature parasympathetic decline: adults born at extremely low birth weight have shown reduced respiratory sinus arrhythmia, a vagal index, compared with their normal-birth-weight peers, raising the question of whether early risk accelerates an age-related drift rather than producing a static deficit. A key limitation acknowledged by the authors is that the included studies were overwhelmingly cross-sectional, so they compare groups at single time points and cannot distinguish true within-individual catch-up growth from survivor bias, in which the frailest infants do not reach later-life follow-up.

Methodologically, the review also pushes back against a common reflex in the field: blaming disagreement on the choice of HRV parameter. According to the authors, timing and etiology, rather than parameter choice, drive the inconsistencies across studies. Whether researchers used time-domain or frequency-domain metrics mattered far less than which perinatal condition was studied and at what developmental stage. That reframing carries practical weight for study design. It argues for age- and condition-specific assessment rather than lumping all at-risk births into one category, and it suggests that a single HRV snapshot at any arbitrary age may mislead more than it informs.

The broader vision connects to the developmental origins of health and disease, the idea that early-life conditions program long-term physiological risk. Autonomic function sits at the crossroads of that program, influencing not only cardiovascular outcomes but also stress reactivity, cortisol regulation, and even social skills and psychopathology, links documented in studies of very preterm children during school age. Wearable devices, which can now capture HRV continuously outside the clinic, promise to turn this research from episodic snapshots into movies of autonomic development, and recent work in healthy preterm-born young adults has already demonstrated the feasibility of such approaches. If validated, HRV could become a kind of early-warning dashboard for NICU graduates, flagging those whose autonomic trajectory warrants cardiology follow-up before blood pressure or metabolic problems emerge.

For now, the authors’ conclusions are deliberately restrained. Autonomic associations with perinatal risk appear condition-specific and age-dependent, and the field needs longitudinal follow-up that follows the same children over time, separating genuine developmental change from the distortions introduced by differential survival. Parents of preterm or growth-restricted children should not read this work as a verdict on their child’s heart. Rather, it is a map of where science should dig next: with growth-restricted children showing the most consistent signatures, infancy emerging as the most revealing window, and adulthood still largely unmapped, the beats between the beats are telling a story, and researchers are finally learning how to read it.

Subject of Research: Heart rate variability after hospital discharge in preterm, low-birth-weight, and growth-restricted populations

Article Title: Heart rate variability after hospital discharge in perinatal risk populations: a systematic review and meta-analysis

Article References: Gistelinck, L., Van den Broeck, R., Verhelst, C., De Vos, M., Wass, S., Naulaers, G., & Boets, B. (2026). Heart rate variability after hospital discharge in perinatal risk populations: a systematic review and meta-analysis. Pediatric Research. https://doi.org/10.1038/s41390-026-05416-3

Image Credits: AI Generated

DOI: 10.1038/s41390-026-05416-3

Keywords: heart rate variability, preterm birth, low birth weight, intrauterine growth restriction, small for gestational age, autonomic nervous system, meta-analysis, neonatology, cardiovascular risk, developmental origins of health and disease, vagal tone, Pediatric Research