The research team, led by Anne H. Zachry of the Department of Occupational Therapy at the University of Tennessee Health Sciences, together with colleagues spanning pediatrics, obstetrics, and preventive medicine, followed 58 infants from early infancy through their first birthday. Caregivers reported when they first introduced tummy time, choosing from prespecified categories ranging from the first two postnatal weeks to two months or older, or never. The infants were then divided into three groups: those introduced to tummy time within the first two postnatal weeks (22 infants), those introduced after the first two weeks (21 infants), and those whose caregivers reported never intentionally introducing it (15 infants). Development was assessed at 3, 6, 9, and 12 months using the Ages and Stages Questionnaire, Third Edition, a standardized parent-completed screening tool that measures communication, gross motor, fine motor, problem-solving, and personal-social skills.

The rationale for probing timing is grounded in developmental science. Prone positioning gives infants early opportunities to practice antigravity head and trunk control, upper-extremity weight bearing, postural adjustments, and active exploration of their environment. The early postnatal period is one of rapid neural and motor development, so introducing prone play during this window could, in principle, provide additional practice opportunities and build tolerance for a position many infants initially resist. Prior studies have consistently linked greater cumulative tummy-time exposure with better motor outcomes. One study of 100 caregivers found that four-month-olds with more tummy time achieved certain prone, supine, and sitting milestones earlier. A systematic review of 16 studies involving 4,237 infants across eight countries associated prone play with greater gross motor development, lower body mass index z-scores, and reduced brachycephaly, although the authors noted that most of the underlying evidence was observational and methodologically limited.

What has been missing is evidence on whether the timing of first exposure, independent of the total amount, makes a measurable difference. The new study addressed this gap directly, comparing infants who began within the first two postnatal weeks against those who began later or not at all, and tracking five developmental domains at four ages across the first year. The researchers used Kruskal-Wallis rank-sum tests, a nonparametric approach appropriate for small groups whose distributions may not meet normality assumptions, to compare score distributions across the three groups. They quantified differences with rank-based eta-squared effect sizes, estimated precision with 95 percent bootstrap confidence intervals built from 2,000 stratified resamples, and applied the Benjamini-Hochberg false-discovery-rate correction across the 20 primary domain-by-age comparisons to guard against spurious findings.

The results were largely null. Of the 20 primary comparisons, three produced unadjusted p-values below 0.05: communication at 6 months, communication at 9 months, and personal-social skills at 9 months. After correction for multiple comparisons, none remained statistically significant. The largest observed effect was for communication at 9 months, with an eta-squared of 0.275 and a 95 percent confidence interval spanning 0.100 to 0.507, followed by personal-social skills at 9 months at 0.213 and communication at 6 months at 0.155. These are nominally moderate to large effect sizes, but the confidence intervals were wide, reflecting the substantial uncertainty inherent in a sample of only 32 infants with complete five-domain data at the 3-, 6-, and 9-month assessments, and 30 infants at 12 months. The remaining comparisons produced effect estimates that were small or near zero, with confidence intervals that generally included zero.

One finding in particular caught the researchers’ attention and illustrates the hazards of overinterpreting small samples. At 9 months, the never-introduced group showed the highest mean personal-social score, at 56.9 with a standard deviation of 4.6, compared with 46.3 for the early-introduction group and 46.1 for the later-introduction group. On its face, this seems to run counter to the premise that earlier tummy time confers advantages. But the authors urge caution: the omnibus test does not establish which groups differ, the corrected p-value was not significant, and the never-introduced subgroup contained only eight infants, making its estimates exquisitely sensitive to sampling variability. The researchers also note that the study was designed to examine timing of introduction, not the independent developmental effects of tummy time itself, so comparisons involving the never-introduced group should not be read as evidence for or against the benefits of prone play.

The authors offer a plausible developmental explanation for why a transient signal might appear at 9 months and vanish elsewhere. Around this age, infants typically achieve independent sitting and increasing mobility, which transforms their opportunities for object exploration, caregiver interaction, and environmental engagement. Emerging motor skills have been linked to development in other domains, including communication and language, in prior work. These rapidly changing experiences could influence personal-social scores regardless of when tummy time began. By 12 months, accumulated motor, social, and environmental experiences may have washed out any early differences. Monthly caregiver reports of positioning, restrictive-equipment use, screen exposure, and interactive play showed broadly overlapping patterns across the tummy-time groups, suggesting that infants who started at different ages may have converged in their later experiences.

The study’s limitations are considerable and the authors are unusually candid about them. Attrition was substantial: only 30 of the 58 enrolled infants, or 51.7 percent, had complete five-domain outcomes at 12 months. Baseline comparisons between families who stayed and those who left revealed potentially meaningful imbalances, with standardized mean differences of 0.93 for maternal education, 0.68 for household income and caregiver marital status, 0.57 for paternal education, 0.49 for infant race, and 0.42 for tummy-time introduction group itself. Such differential loss to follow-up raises the risk of attrition bias, meaning the retained sample may not represent the original cohort. Both the exposure, the timing of first tummy time, and the outcome, the ASQ-3, were caregiver-reported, introducing the possibility of recall error and common-method bias. The broad later-introduction category also lumped together infants first exposed at ages ranging from two weeks to two months or older, so the actual temporal contrast between some early and later participants may have been only a few weeks, possibly too small to produce detectable differences on a broad screening instrument.

There is also the matter of what happens after introduction. The study did not standardize subsequent tummy-time practices, so infants who began later may have accumulated similar total exposure by mid-infancy, eroding any differences attributable to timing alone. Infant development is multifactorial, shaped by temperament, tolerance for prone positioning, growth, birth order, parental education, socioeconomic conditions, caregiver-infant interaction, opportunities for unrestricted movement, equipment use, screen exposure, sleep, and environmental stimulation. The sample was too small to support a stable multivariable model adjusting for these factors, meaning residual confounding is likely. The researchers calculated that a properly powered confirmatory study with three similar groups, a two-sided alpha of 0.05, 80 percent power, and a moderate effect size would require approximately 53 participants per group, or about 159 in total, rising to roughly 200 with an anticipated 20 percent attrition.

Importantly, the authors emphasize that current recommendations supporting supervised prone play should not be reconsidered based on these pilot findings. The study was never designed to evaluate whether tummy time itself benefits development, a question already addressed by a substantial prior literature, but rather whether the timing of first introduction matters. The answer, for now, is that there is no clear evidence of reproducible developmental differences by timing, and also no evidence that timing is irrelevant. The findings are best read as a map of uncertainty: preliminary patterns, wide confidence intervals, and a clear agenda for future research. Larger prospective studies with objectively documented exposure, detailed longitudinal measurement of tummy-time dose and quality, and prespecified covariate-adjusted analyses will be needed to determine whether the first fortnight of life truly represents a developmental window for prone play, or whether what matters most is simply the tummy time that follows.

Subject of Research: The relationship between the timing of tummy-time introduction in infancy and developmental outcomes during the first year of life

Article Title: Timing of tummy-time introduction and developmental outcomes during the first year of life: an exploratory pilot study

Article References: Zachry, A. H., Abdullah, F., Assfoura, R., Berke, T., Boushra, M., Ghaly, A., Khalil, M., Woods, L., & Zhao, C. (2026). Timing of tummy-time introduction and developmental outcomes during the first year of life: an exploratory pilot study. Frontiers in Pediatrics, 14, Article 1923077. https://doi.org/10.3389/fped.2026.1923077

Image Credits: AI Generated

DOI: 10.3389/fped.2026.1923077

Keywords: tummy time, infant development, ASQ-3, motor milestones, prone positioning, pilot study, pediatrics, developmental screening, attrition bias, caregiver report, American Academy of Pediatrics, early childhood

Spinal muscular atrophy is caused by mutations in the SMN1 gene, which deprives spinal motor neurons of functional survival motor neuron (SMN) protein. The resulting degeneration produces progressive weakness of skeletal muscles and, in the most severe form, compromises breathing and swallowing. Before disease-modifying therapies existed, children with SMA type I — defined by symptom onset within the first six months of life and an inability to sit unsupported — almost invariably died or required permanent mechanical ventilation by 20 months of age. The introduction of onasemnogene abeparvovec, which delivers a functional copy of SMN1 directly to motor neurons via an AAV9 vector, fundamentally changed this trajectory. In pivotal trials such as STR1VE and SMART, which enrolled carefully selected infants under six months without bulbar or respiratory complications, survival rates climbed to between 90 and 100 percent and most infants gained the ability to sit.

Real-world experience, however, has always been more complicated. Once the therapy became commercially available, its approved label expanded well beyond the narrow trial population, allowing treatment of older and heavier infants, children with bulbar and respiratory impairment, and patients who had already been exposed to other disease-modifying therapies such as nusinersen or risdiplam. These broader cohorts have shown greater variability in outcome: while survival and motor gains remain the norm, not every child achieves independent sitting within the first year, and older, heavier children tend to respond less robustly. Recognizing that some milestones may simply take longer to emerge, the Italian research consortium set out to determine whether extended follow-up would reveal continued functional progress that shorter studies had missed.

The new analysis draws on the Italian SMA Consortium (ITASMAC) registry and includes all consecutive symptomatic type I patients treated with onasemnogene abeparvovec who completed at least 24 months of follow-up, regardless of SMN2 copy number, age or weight at treatment, prior therapy, or sex. The cohort of 64 children was divided into three groups based on treatment history: 27 received the gene therapy as monotherapy, 9 received a short bridging course of nusinersen or risdiplam for less than three months before switching, and 28 had been treated with another disease-modifying drug for a median of nearly two years before transitioning to the gene therapy. Motor function was assessed with the validated CHOP-INTEND scale, and milestone acquisition, nutritional status, and respiratory support were documented prospectively at each clinical visit across the two-year observation window.

The baseline characteristics of the three treatment groups differed markedly, reflecting the realities of sequential therapy in clinical practice. Children treated with the gene therapy alone were the youngest, with a mean age at infusion of just 0.33 years, while those who switched from prior therapy were significantly older at a mean of 2.92 years. Switch patients also entered with the highest baseline CHOP-INTEND scores — a mean of 47.8 compared with 30.6 among monotherapy patients — because their earlier treatment had already partially stabilized their motor function. To disentangle these overlapping variables, the researchers built two separate multivariable linear mixed-effects models, one anchored to pretreatment status and one to chronological age at infusion, both adjusting for baseline motor score and SMN2 copy number.

Across the entire cohort, motor scores improved dramatically, rising on average by roughly 20 CHOP-INTEND points per year of follow-up. Yet the pace of improvement was not uniform. Children who switched to the gene therapy after prolonged prior treatment improved significantly more slowly than those treated without prior exposure, a difference that persisted even after accounting for their higher starting scores. Similarly, in the age model, each additional month of age at infusion was associated with a measurable slowing of the rate of motor gain. The researchers caution that age and pretreatment status are so strongly intertwined in this observational dataset that the independent contribution of each factor cannot be definitively separated — older children were, almost by definition, the ones who had spent more time on prior therapies. Both patterns may simply reflect that children who received early prior treatment had already captured much of their achievable therapeutic benefit before the gene therapy was administered.

The milestone data paint a striking picture of how timing shapes outcome. Of the 49 children who could not sit at the time of infusion, 40 — or 80 percent — achieved independent sitting during the two years of follow-up, and 5 achieved independent walking. Crucially, 12.5 percent of those who gained sitting did so only after the 18-month mark, well beyond the window captured by earlier trials, confirming that meaningful motor gains continue into the second year and that premature judgments about treatment failure may be unwarranted. Every child treated before six months of age who carried three copies of the SMN2 modifier gene achieved sitting within the age-appropriate physiological window. In contrast, among infants with two SMN2 copies, outcomes ranged from on-time sitting to never achieving the milestone, with low baseline CHOP-INTEND scores and the presence of bulbar or respiratory impairment most consistently associated with less favorable trajectories, though not invariably so for every individual child.

Bulbar and respiratory function also evolved favorably for many children. Of the 54 children fed orally at the time of treatment, only 3 required a feeding tube during follow-up, while 2 of the 10 who already had tubes successfully transitioned back to oral feeding. On the respiratory front, none of the 43 children already requiring ventilatory support at baseline progressed to tracheostomy, and 3 were ultimately weaned off ventilation altogether. Among infants who entered treatment with no evident respiratory or bulbar impairment, fewer than 5 percent needed a gastrostomy and only 12 percent required non-invasive ventilation over the two-year period. Safety surveillance throughout the second year after treatment identified no adverse events, and the authors note that no new safety signal emerged between the first and second years, consistent with prior international reports.

Set against the natural history of the disease, the results are transformative. Untreated children with SMA type I never achieve independent sitting, and more than 90 percent die or require permanent ventilation by age two. In this cohort, fewer than 20 percent of the children who could not sit at treatment failed to gain that milestone within two years. The authors acknowledge the interpretive limits of their observational design — confounding by indication, selection bias, and the entanglement of age with treatment history all complicate attribution, and larger cohorts with methods such as propensity score matching would be needed to fully resolve them. Even so, the findings carry a clear clinical message: two years after a single infusion, children with the most severe form of spinal muscular atrophy continue to gain function, milestones once considered unattainable are achieved, and the duration of follow-up matters when judging the true efficacy of this therapy. Future studies, the researchers suggest, should extend to cognitive, behavioral, and language outcomes to fully characterize the long-term neurodevelopmental trajectory of these gene therapy-treated children.

Subject of Research: Long-term efficacy of onasemnogene abeparvovec gene therapy in type I spinal muscular atrophy

Article Title: Onasemnogene Abeparvovec in Type I Spinal Muscular Atrophy: 24‐Month Follow‐Up From the Italian Registry

Article References: Pane, M., Coratti, G., Cutrì, C., Varone, A., Masson, R., D'Amico, A., Sansone, V., Messina, S., Ricci, F., Ticci, C., Bruno, C., Agosto, C., Benedetti, F., Pini, A., Siliquini, S., Filosto, M., Zambon, A., Bitetti, I., Manna, M. R., … the ITASMAC working group (2026). Onasemnogene Abeparvovec in Type I Spinal Muscular Atrophy: 24‐Month Follow‐Up From the Italian Registry. Annals of Clinical and Translational Neurology, 13(9), 1866-1877. https://doi.org/10.1002/acn3.70356

Image Credits: AI Generated

DOI: 10.1002/acn3.70356

Keywords: spinal muscular atrophy, gene therapy, onasemnogene abeparvovec, SMN1, AAV9 vector, CHOP-INTEND, motor milestones, Italian registry, nusinersen, risdiplam, real-world data, pediatric neurology