Preterm birth, defined by the World Health Organization as delivery before 37 completed weeks of gestation [1], confers marked vulnerability due to physiological immaturity and enduring misconceptions, such as the belief that neonates, particularly preterm infants, do not fully experience pain. These notions have been unequivocally refuted, with evidence showing that even very premature infants perceive and respond to painful stimuli [2].

The perception of pain in preterm infants is complex and clinically significant. The central nervous system begins to develop early in gestation, and although the nociceptive system is not fully mature at birth, it is functional from as early as 20–24 weeks of gestation [3,4]. Peripheral nociceptors and ascending pathways are active at this stage, but inhibitory circuits remain immature, resulting in heightened sensitivity to painful stimuli. The gradual process of myelination and the ongoing maturation of brain structures such as the thalamus and somatosensory cortex further influence how pain is processed. Consequently, preterm infants may display exaggerated or prolonged responses to pain when compared to full-term infants [3].

Pain in the neonatal period is not only perceived by newborns, including those born preterm, but also elicits significant physiological and neuroendocrine responses with both immediate and long-lasting consequences. These responses include alterations in heart rate, oxygen saturation, blood pressure, hormonal profiles, and metabolic activity [5]. Acutely, repeated painful experiences may compromise neuronal development, modulate stress reactivity, and influence subsequent behavioral responses, reinforcing the definition of pain as an unpleasant sensory and emotional experience linked to actual or potential tissue injury [5,6]. Recent evidence has demonstrated that early neonatal pain exposure is associated with altered physiological outcomes, including later dysregulation of cortisol levels in childhood. In neonatal intensive care units (NICUs), preterm infants are frequently subjected to multiple invasive procedures that may generate pain, leading to behavioral stress and adverse physiological outcomes [7–9].

Accurate and systematic pain assessment is therefore essential for ensuring safe and effective pain management in preterm infants. More than 40 neonatal pain assessment tools have been developed, yet only a few are routinely applied in clinical practice. Among these, the Neonatal Facial Coding System (NFCS) is one of the most well-established and widely used instruments. It evaluates facial expressions as indicators of pain, and scores of 3 or higher (NFCS ≥ 3) are typically interpreted as evidence of pain [10,11].

While pharmacological treatments remain central to neonatal pain management, non-pharmacological strategies have been increasingly recognized as valuable adjuncts. Hydrotherapy is a therapeutic intervention involving controlled immersion in warm water, which promotes muscle relaxation, reduces stress responses, and supports autonomic regulation by simulating the intrauterine environment. Hammock positioning (redotherapy) is a positioning technique designed to provide postural containment and flexion, facilitating physiological stability and behavioral organization. Both interventions aim to support neonatal homeostasis, defined as the ability to maintain stable cardiorespiratory, thermal, and neurobehavioral functions in response to environmental stressors. These techniques have been increasingly employed in preterm infants to reduce stress, improve comfort, and provide analgesic effects [12–15].

Despite growing interest in these non-pharmacological approaches, there remains a lack of randomized clinical trials directly comparing the isolated and combined effects of hydrotherapy and hammock positioning on pain reduction during routine painful procedures in preterm neonates. This gap underscores the necessity of conducting the present study.

Given this context, the present study seeks to evaluate the effects of hydrotherapy and hammock positioning, both individually and in combination, on the reduction of pain in hospitalized preterm neonates.

The present study demonstrated that hydrotherapy, hammock positioning, and the combination of these two techniques were effective in reducing pain scores in preterm neonates.

A total of 45 preterm neonates were included in the analysis, with 15 allocated to each intervention group. The groups were comparable at baseline with respect to key demographic and clinical characteristics (Table 1). There were no statistically significant differences among the three groups regarding sex distribution (p = 0.84), mean gestational age (p = 0.78), birth weight (p = 0.91), postnatal age at enrollment (p = 0.83), or type of feeding (p = 0.89). The overall sample consisted of 24 male neonates (53.3%) and 21 female neonates (46.7%), with a mean gestational age of 32.4 ± 2.1 weeks and a mean birth weight of 1,720 ± 310 g. All neonates were receiving enteral feeding via an orogastric tube at the time of enrollment. These findings indicate that the intervention groups were clinically homogeneous at baseline.

Following hydrotherapy, neonates showed a significant reduction in pain, as evidenced by a decrease in NFCS scores from 3.98 ± 1.65 to 2.02 ± 1.06 (p < 0.0001; Table 2). Before hydrotherapy, 78.7% of neonates presented with pain, while after the intervention, only 28.4% had an NFCS score ≥ 3 (p < 0.0001; Table 3).

For neonates undergoing hammock positioning, mean pain scores decreased from 3.01 ± 1.49 to 2.03 ± 1.11 after the intervention (p < 0.0001; Table 2). Prior to this intervention, 56% of neonates exhibited pain, whereas after the intervention, only 32.4% did (p < 0.0001; Table 3).

When neonates received hydrotherapy followed by hammock positioning, pain scores also improved, decreasing from 3.40 ± 1.59 to 1.87 ± 0.87 (p < 0.0001; Table 2). In this group, 66.7% of neonates initially presented with pain, compared with only 18.7% after the intervention (p < 0.0001; Table 3).

Exploratory analyses did not demonstrate significant associations between demographic variables (sex, gestational age, birth weight, postnatal age, or type of feeding) and the magnitude of pain reduction within any intervention group (all p > 0.05), suggesting that the analgesic effects observed were independent of baseline neonatal characteristics.

Consistent with the study objective, statistical analyses were limited to within-group comparisons before and after each intervention. Direct between-group comparisons of intervention efficacy were not performed.

The most important finding of this randomized clinical trial is that hydrotherapy, hammock positioning, and the combination of the two interventions significantly reduced pain in preterm neonates, as measured by the Neonatal Facial Coding System (NFCS). Importantly, pain scores decreased to values below the validated cut-off for pain, indicating not only statistical but also clinical relevance. Across 1,350 pain assessments performed in 45 preterm neonates over 15 consecutive days, these findings provide robust evidence supporting the effectiveness of these non-pharmacological interventions in neonatal pain management.

Both interventions were effective when applied individually, and the combined intervention produced comparable analgesic benefits, suggesting that hydrotherapy and hammock positioning act as complementary comfort strategies rather than competing modalities. The consistent reduction in NFCS scores before and after each intervention supports their role as reliable adjuncts to routine neonatal care during painful or stressful aspects of routine neonatal care.

The present results are consistent with prior research demonstrating the benefits of hammock positioning. Queiroz et al. (2018) [17], for instance, showed that both hammock and prone positioning reduced NFCS scores in 20 preterm infants, although their study included only 40 pain assessments. Similarly, Giamellaro et al. (2018) [18] observed a significant reduction in pain intensity among ventilated neonates using hammock positioning, but their findings were based on only 16 measurements. Ribas et al. (2019) [19] reported improvement using the Premature Infant Pain Profile (PIPP), but not the NFCS, highlighting how outcomes may vary depending on the pain assessment instrument employed. Conversely, Jesus et al. (2018) [14] did not detect significant benefits, which may be attributable to methodological differences, shorter intervention duration, and a smaller sample size.

With respect to hydrotherapy, these findings align with those of Vignochi et al. (2010) [20], Silva et al. (2016) [21], and Cecconello et al. (2010) [22], all of whom demonstrated significant reductions in neonatal pain or stress indicators following aquatic interventions. Compared with these studies, the present trial included a larger number of repeated pain measurements, strengthening the reliability of the observed effects. In contrast, de Oliveira Tobinaga et al. (2016) [23] reported improvements in physiological stress markers, such as reduced salivary cortisol and stabilized vital signs, without significant changes in NIPS pain scores, underscoring the complexity of neonatal pain assessment and the importance of using validated, behavior-based tools such as the NFCS.

Hydrotherapy and hammock positioning offer several practical advantages: they are low-cost, easy to implement, and associated with minimal risk when performed by trained professionals. Given the well-documented risks of pharmacological analgesia in neonates — including respiratory depression, feeding intolerance, urinary retention, and potential long-term neurodevelopmental effects [24,25], non-pharmacological strategies should be prioritized whenever possible. Morphine, although frequently used in NICUs, has been associated with later behavioral disturbances, including anxiety, depression, and attention deficits [26]. Even non-opioid analgesics are prescribed cautiously in this population, with acetaminophen remaining the only widely accepted option [27].

Established non-pharmacological interventions, such as skin-to-skin contact, breastfeeding, oral sucrose, and non-nutritive sucking, have demonstrated efficacy in reducing procedural pain in neonates [28–30]. The present study further expands this evidence base by supporting hydrotherapy and hammock positioning as additional, evidence-based options for neonatal comfort and pain modulation.

The strengths of this study include the large number of pain assessments (n = 1,350), the use of a validated and widely recognized pain assessment tool (NFCS), and the evaluation of both individual and combined non-pharmacological interventions. However, several limitations should be acknowledged. First, the study was conducted at a single center, which may limit generalizability. Second, although standardized training was provided, facial expression–based assessments are inherently subject to some degree of inter-rater variability. Third, the analysis focused on short-term pain outcomes, and long-term effects on neurodevelopment, stress regulation, and behavioral outcomes were not evaluated. Future studies should therefore investigate whether repeated exposure to these interventions yields sustained benefits beyond the neonatal period.

Overall, the findings of this study support the incorporation of hydrotherapy and hammock positioning into standardized pain management protocols in neonatal intensive care units. Future research should explore the potential synergistic effects of combining these interventions with other evidence-based non-pharmacological strategies, such as kangaroo care or oral sucrose, and assess long-term outcomes, including neurodevelopmental trajectories and caregiver – infant bonding.

In conclusion, hydrotherapy and hammock positioning, applied individually or in combination, are effective, safe, and feasible strategies for reducing pain in preterm neonates. Their integration into routine NICU practice may reduce reliance on pharmacological analgesia and contribute to safer, more holistic neonatal care.

None.

Ana Talita Vasconcelos Arcanjo Ribeiro da Silva: Conceptualization, data curation, formal analysis, investigation, methodology, validation, visualization, writing original draft, writing review & editing.

Francisco Placido Nogueira Arcanjo: Project Administration, conceptualization, data curation, formal analysis, investigation, methodology, validation, visualization, writing original draft, writing review & editing.

Jeferson de Sousa Justino: Data curation, formal analysis, investigation, methodology, validation, visualization, writing original draft, writing review & editing.

Lizandro de Andrade Teles: Data curation, formal analysis, investigation, methodology, validation, visualization, writing original draft, writing review & editing.

Ana Kelly Melo de Aquino: Data curation, formal analysis, investigation, methodology, validation, visualization, writing original draft, writing review & editing.

All authors participated in validation, visualization, writing the original draft, writing review & editing.

The contents underlying the research text are included in the manuscript.