Globally, 1 in 10 infants is born preterm (<37 weeks gestation). Preterm birth rates have remained relatively stable over the past decade, although they have increased in some regions. In 2020, it was estimated that approximately 1 million newborns would die as a result of preterm birth problems, and millions more would live with disabilities that affect them and their families for the rest of their lives (1).

Preterm infants often spend their early weeks or months in the Neonatal Intensive Care Unit (NICU), an environment vastly different from the intrauterine milieu. NICUs expose infants to intense lighting, excessive noise, and painful procedures, all of which can disrupt brain development, neural network connectivity, and physiological responses (2). Consequently, preterm infants face significant risks in sensory, motor, emotional, cognitive, and social development, particularly those born before 34 weeks of gestation (3–5). Moreover, preterm birth increases stress, anxiety, and depression levels in families and imposes considerable medical and socioeconomic burdens on society.

Early intervention (EI) is crucial in supporting the development of preterm infants who face developmental risks (6). EI is defined as services provided to enhance brain connections during critical periods of an infant's central nervous system development, particularly from birth to 3 years of age (6, 7). For decades, EI has been implemented worldwide to improve long-term positive outcomes in infants' development and family well-being. However, the literature has not consistently reported the effectiveness of EIs in improving infant development (8). Possible reasons for this discrepancy may include the type of intervention, inadequate intervention dosage, timing of intervention initiation, and the efficacy of the intervention.

One of the types of EI for gross and fine motor development provided by physical and/or occupational therapists is traditional treatment (TT), which is commonly recognized worldwide as being based on neurodevelopmental therapeutic principles, and focusing on balance and correction reactions, weight-bearing, and postural control (9, 10). However, new intervention approaches are required because TT is traditionally a “hands-on” method where the physio or occupational therapist engages directly with the child, manipulates their position, and plays the role of a teacher in the relationship with the infant and caregiver. In this approach, active and continuous engagement on the part of the child remains limited because such stimuli can only be provided during therapy sessions in the clinic and through recommendations given to families for home practice.

Recent models of EI have been increasingly shaped by insights derived from enriched environment (EE) research and ecological theories of development (11–16). Findings from EE studies, particularly those conducted in animal models, have consistently demonstrated that systematic environmental enrichment can exert profound influences across multiple domains, including developmental trajectories, behavioral adaptation, physiological regulation, neuroanatomical organization, and even molecular processes (17–20). In animal research, despite variations in specific methods and emphases, enrichment paradigms have relied on a common set of ten principles—physiological homeostasis, safety, multisensory stimulation, spatial characteristics of the environment, novelty, challenge, enjoyment, sustained engagement, social opportunities, and active exploration—as the primary dimensions through which enrichment is operationalized) (21, 22). Building on this evidence base, recent EI approaches selectively integrate different combinations of these principles while also drawing upon diverse ecological frameworks of human development. This dual grounding enables programs to establish a shared conceptual foundation, yet the particular constellations of principles and theoretical orientations they adopt vary considerably. Such variability reflects distinct emphases in how developmental processes are conceptualized, how experiential contexts are organized, and how implementation strategies are prioritized in practice (22–24).

EE-based EI approaches aim to enhance neurodevelopment by increasing multisensory stimulation, opportunities for physical activity, and social engagement, primarily through the encouragement of spontaneous exploratory behaviors (22, 23, 25). Contemporary programs such as GAME and START-Play exemplify evidence-based applications of ecological principles. The GAME program, grounded in motor learning and Dynamic Systems Theory (DST), emphasizes goal-oriented, intensive motor training delivered in the home environment. Families collaborate with therapists to set individualized developmental goals that encompass both motor development and broader health-related factors such as sleep and nutrition. Motor tasks are scaffolded to encourage active, self-initiated movements, while parents are coached to observe, support, and problem-solve, thus integrating variability and progressive challenge within structured home programs (14). Similarly, START-Play, informed by principles of Embodied Cognition, is delivered in the infant's natural environment and combines motor challenges with early cognitive constructs. Caregivers provide social support, scaffold learning, and facilitate active engagement in “just-right” challenges (13). Viewed through the lens of EE principles, both interventions incorporate multiple domains such as active exploration, social opportunities, and sustained engagement; however, they assign comparatively less emphasis to aspects like homeostasis, safety, spatial features of the environment, and certain dimensions of multisensory stimulation. Importantly, even when grounded in similar EE principles, the two approaches interpret, prioritize, and operationalize these principles differently, reflecting the distinct theoretical perspectives from which they emerge.

The HEP Approach, developed by Balıkcı, builds on the foundations of EE by offering a comprehensive framework that systematically incorporates all ten core principles (22). It is designed as a clinic-based intervention and parent coaching model which is provided with parallel parent-directed activity implementation in the home contexts; and therapist monitoring of infants' natural environments through online follow-up. Provision of the intervention initially in the clinic provides several advantages: infants are exposed to an already EE with diverse sensory and motor opportunities, while parents receive structured coaching in a supportive setting. Following the clinic sessions, families transfer and adapt the coached strategies into their daily routines and natural contexts, supported by online follow-up, which serves to guide, reinforce, and sustain this integration in the home environment. The HEP Approach is grounded in multiple theoretical perspectives, including Gibson's Ecological Perception Theory, Perception-Action Theory, Sensory Integration, and the Person–Environment–Occupation (PEO) Model, Dynamic Systems Theory (DST), Neuronal Group Selection Theory (22–24). In line with evidence supporting family-centered, goal-oriented, and coaching-based practices in pediatric occupational therapy (26–28), the HEP Approach empowers caregivers through structured yet flexible strategies that foster co-regulation, sensory–motor development, and environmental adaptation. In practice, homeostasis is prioritized, with Dynamic Systems and Sensory Integration theories suggesting that regulation in this domain can facilitate progress across other developmental areas. Families are guided in strategies such as rhythmic rocking, adjusting voice tone, or narrating daily events to enhance self-regulation. From the perspectives of Sensory Integration and Perception–Action theories, this approach underscores the importance of leveraging a child's strongest sensory systems for learning and development, supported by targeted environmental modifications—for instance, positioning infants with strong visual or auditory abilities in upright postures to enhance engagement. For infants at increased risk, delayed motor development may restrict opportunities for independent floor-based exploration. By facilitating upright positioning, caregivers not only enhance infants' sense of security through greater environmental control but also enable active tactile and auditory exploration with the hands which can address developmental sensory and motor challenges. In this way, structured environmental adaptations and carefully designed activity opportunities create enriched contexts for discovery that simultaneously support sensory processing, praxis, and broader developmental outcomes.

Based on the PEO model and Sensory Integration theory, spatial features of the environment and the objects therein are organized to provide safe, “just-right” challenges, such as placing a non-sitting infant in a supportive basket to encourage exploration with hands and eyes. In addition, activities and objects are analyzed for sensory features and praxis challenges to provide just-right and adaptive opportunities for interaction. Similarly, consistent with Perception–Action principles, activities and environments are structured to maximize opportunities for active exploration and self-initiated movement, for instance, through the use of baby walkers or bouncers to promote mobility in infants with restricted motor control. By integrating these theoretical perspectives with the core principles of EE into a unified and ecologically valid framework, the HEP Approach introduces a distinctive combination of practices to the field of early intervention. Supplementary Table S1 provides a point-by-point comparison of these three interventions to illustrate the differences and similarities of the approaches (Supplementary Table S1).

This study hypothesizes that the HEP Approach will demonstrate greater effectiveness in improving motor skills and sensory functions of preterm infants with increased developmental risk and a corrected age between 4 and 10 months compared to TT. Furthermore, it posits that the HEP Approach will better address caregiver anxiety by fostering active parental involvement in the intervention process.

This study investigated the effects of the HEP Approach on motor and sensory development in preterm infants and parental anxiety relative to TT. Data from 29 of the 32 randomized infants were evaluated. The average gestational age suggested a cohort of preterm infants at increased developmental risk (38, 39). Except for maternal age, the groups were sociodemographically analogous. Following a 12-week period, both therapies enhanced infant outcomes and alleviated parental anxiety, with the HEP Approach producing markedly superior improvements in motor and sensory scores.

At baseline, it was observed that the infants' pre-treatment mean scores for stationary, locomotion, and grasping were below the normative data, indicating delayed motor skill development compared to full-term infants (38, 40). In motor skills, infants demonstrated statistically significant improvement in all subtests and PDMS-2 quotient scores, with a large effect size, over time.

The TT intervention often encompasses activities aimed at enhancing righting and balance reactions, as well as facilitating trunk control. The literature indicates that TT is expected to enhance motor development, particularly reflexes and stationary skills (9, 41). Consistent with previous studies, TT was found to effectively improve postural control and balance over time (41, 42). Moreover, substantial changes in fine motor (grasping and visual-motor skills) scores indicate that improved postural control promotes manipulative skills over time, consistent with previous research findings (43).

For the HEP Approach group, it was hypothesized that the significant improvements in the gross, fine, and total motor skills of preterm infants could be attributed to the collaboration between the therapist and the family. This collaboration ensures that the child receives continuous, individualized environmental stimulation, encouraging active exploration and participation. This hypothesis is supported by previous studies demonstrating the positive outcomes of the HEP Approach on motor development in infants (22–24). Additionally, prior case reports have shown that motor development in infants with cerebral palsy improved following HEP Approach intervention (23, 24). Furthermore, a recent feasibility study revealed that the HEP Approach improved motor development in premature infants at developmental risk (24).

Upon comparing the groups, the HEP Approach was found to be superior to the TT intervention in improving fine motor, gross motor, total motor scores, and all other PDMS-2 subscales, except for reflexes and stationary. This similarity in reflex and stationary subscales may be attributed to the distinct focus of each intervention. The TT intervention is specifically designed to improve reflex responses, balance reactions, and postural control, which probably explains its direct effectiveness in these areas. In contrast, the HEP Approach indirectly creates opportunities that facilitate reflex development and stationary skills through family-led continuous, individualized environmental adaptations and activity choices. This suggests that the HEP Approach may serve as an effective alternative to TT for supporting reflex and stationary motor skills. However, for other subscales, including grasping, locomotion, and visual-motor integration, the HEP Approach demonstrated more significant improvements.

The reason for this superiority may lie in the more targeted, dynamic, and personalized nature of the HEP Approach. Unlike TT, which focuses on general postural control and balance, the HEP Approach provides continuous and individualized environmental stimulation tailored to the needs of each infant, thus fostering more effective motor development (22–24). Numerous studies support the importance of the environment, objects, and interactions with people in promoting motor development (44–50). For instance, Hewitt et al. demonstrated the positive effects of environmental modification and appropriate object use on tolerance to the prone position, which directly impacts locomotion development (51). Other studies have also found that placing infants on inclined surfaces with a preferred object increases head lifting in the prone position, promoting gross motor development (52–54). Similarly, Morgan et al. and Dusing et al. observed that providing appropriate toys, organizing the environment, and supporting infant movements positively enhanced motor skills (55).

In the HEP Approach, it is crucial to facilitate the utilization of infants' strongest sensory systems (24). Therefore, the objective is to position infants with sufficient visual perception in a vertical position (either sitting or standing), enabling them to develop improved awareness of their bodies and environment (22–24). This, in turn, enhances their ability to use their bodies and engage with their environment. Furthermore, numerous studies have shown that vertical positions are linked to hand-eye coordination, manipulation skills, joint attention, reaching, and grasping abilities (22, 56–60). Kretch et al. investigated the relationship between sitting and infants' exploration and interactions in typically developing infants aged 4–7 months and infants with motor development delays aged 7–16 months. Findings demonstrated that supported infants in both groups interacted less with their caregivers (by looking away more) and objects (by grasping and touching them less) than unsupported infants during free play. At the same time, caregivers who had to support their infants with both hands were also less able to use objects for interaction (57). Harbourne et al. also found that the fine motor skills of infants with motor delays improved after 12 weeks of the START-Play intervention. The researchers suggested that this improvement in fine motor skills was related to the infants' early vertical positioning (61).

According to the evaluation of sensory functions with the TSFI, the infants' baseline AMF, RVS, and Total Scores in this study in both groups were found to be at risk or deficient depending on their age. Similarly, Cabral et al. found that preterm infants had lower RTDP and Total Scores than term infants in sensory functions evaluated with TSFI (62). These results suggest that early interventions should focus on both sensory functions and motor skills in preterm infants.

Infants showed statistically significant improvement in all domains of the TSFI (RTDP, AMF, VTI, OMC, RVS, and Total Scores), with large effect sizes over time. Improvements in sensory functions within the TT intervention over time are thought to arise from vestibular, proprioceptive, and tactile sensory inputs produced during therapeutic handling activities. Similarly, Habik-Tatarowska found that a four-month intervention, similar to the TT intervention in this study, had a positive effect on the sensory functions of infants aged 4–12 months (63). Thus, the significant improvements observed in TT may be attributed to these sensory experiences. In the HEP Approach, while no direct sensory activities were performed, the results were consistent with our hypothesis that sensory improvements could result from the infant's increased capacity for movement and active exploration (22–24). According to the Perception-Action Theory, sensory functions and motor skills are intrinsically linked, with perception informing motor activity and motor development enhancing sensory experiences (44, 45). Research by Adolph and Franchak supports this, noting that motor behavior enriches perceptual experiences and offers feedback that influences subsequent actions (64). Additionally, Adolph and Hoch suggested that motor development facilitates learning and exploration, promoting developmental changes across several domains (44). In this study, the HEP Approach likely improved sensory functions by enhancing the infants' movement abilities, which fostered sensory experiences and integration. These findings also align with sensory integration theory, which emphasizes the critical role of sensory inputs in development, including motor skills (65, 66).

When comparing the groups, the HEP Approach demonstrated significant improvement in sensory functions, including AMF, VTI, and Total Scores, with large effect sizes favoring the HEP Approach group. This is especially notable because sensory improvements were not a direct target of the intervention. It was hypothesized that these improvements were due to the increased sensory experiences provided by the infants’ enhanced movement capacity and active exploration. Despite the absence of direct sensory activities, the HEP Approach indirectly improved sensory functions through its focus on motor skills, highlighting the relationship between sensory and motor development (44, 64). These results align with studies emphasizing the importance of environmental stimulation in fostering both motor and sensory development in preterm infants (44–50).

The similarity in improvements over time for RTDP, OMC, and RVS subtests in both groups may be attributable to the characteristics of the therapies. Vestibular and tactile inputs from therapeutic handling activities commonly employed in TT intervention are believed to enhance these domains directly. The HEP Approach posits that an infant's spontaneous engagement with various sensory stimuli through active exploration indirectly fosters development in these domains. The HEP Approach, which yields comparable outcomes for advancing these areas, may serve as an alternative to the TT intervention.

These findings align with the broader literature, which underscores the relationship between motor development and sensory functions in preterm infants (63, 64). These results, particularly the improvement in sensory functions within the HEP Approach group, support previous studies suggesting that early interventions focusing on motor skills can also lead to significant gains in sensory functions (16, 22–24). The HEP Approach, by facilitating movement and active exploration, plays a key role in promoting both motor and sensory development, thus enhancing overall developmental outcomes for preterm infants.

Parents' adverse mental health, particularly anxiety, is a critical factor due to its adverse effects on infants' sensory functions, motor skills, and overall developmental progress (65, 67). Anxiety in caregivers can create a stressful environment that may hinder their ability to provide optimal care, which in turn can impact their child's growth and development. A systematic review and meta-analysis have indicated that preterm infant development is more closely associated with the anxiety levels of caregivers than their stress levels (68). Therefore, addressing the anxiety of caregivers from a holistic perspective is essential in early intervention studies to promote both the parent's well-being and the infant's development.

In this study, the mean anxiety level of the parents at baseline was mild, with a BAI score of 13.93. This indicates that, while the parents did experience anxiety, it was within the mild range at the beginning of the intervention. Given the challenges of caring for preterm infants, such as increased medical appointments and constant worry about their child's health, it is common for parents to experience heightened anxiety during the early stages. This finding aligns with the existing literature, where parents of preterm infants often report higher anxiety levels due to the increased uncertainty and challenges associated with caring for their vulnerable infants (68, 69).

At the end of the intervention, there was a significant reduction in anxiety scores for all participants, with large effect sizes observed. This indicates that both the HEP Approach and TT interventions were effective in reducing parental anxiety. However, when comparing the two groups, no significant interaction between group and time was found. This suggests that while both interventions resulted in significant reductions in caregiver anxiety, there was no marked difference in the extent of improvement between the two groups.

These findings suggest that early interventions for preterm infants can significantly reduce caregiver anxiety, even when baseline anxiety levels are mild. Both the HEP Approach and TT interventions were similarly effective in addressing caregiver anxiety. This supports the broader literature on family-centered interventions, which emphasizes the importance of caregiver mental health in improving both parent and infant outcomes (65, 67, 70). Future research could explore additional factors to enhance the efficacy of these interventions and further improve caregiver well-being.

The HEP Approach closely aligns with the fundamental principles of occupational therapy, particularly in its emphasis on promoting meaningful participation, enhancing functional outcomes, and utilizing activity-based and family-centered practices. From an occupational therapy standpoint, the HEP Approach transcends mere skill learning by facilitating infants' engagement in meaningful activities within enriched and ecologically relevant environments. The HEP Approach's organized yet adaptable framework enables caregivers to modify the physical and social environment to facilitate the infant's active participation, self-regulation, and sensory-motor development. This reflects the emphasis of occupational therapy on enabling individuals to participate in daily routines and meaningful occupations across settings. Moreover, the incorporation of parental coaching, environmental adjustments, and infant-led exploration within the HEP Approach aligns with the PEO model commonly utilized in occupational therapy. These findings support the view that the HEP Approach is not only effective in improving developmental outcomes but also embodies occupational therapy principles in both philosophy and practice.

This study offers valuable insights into the effectiveness of the HEP Approach in preterm infants; however, several limitations exist. The sample consisted of preterm infants with a mean gestational age of 28.9 weeks and a mean current age of 6 months, as well as parents with a relatively high level of education. Additionally, infants with grade III/IV intraventricular hemorrhage or significant sensory impairments were excluded to maintain methodological rigor and a relatively homogeneous sample for this study. Although referrals came from three different hospitals, all participants were from a single geographical region and received assessment and intervention at the same center, which may reflect limited cultural and healthcare variation. These clinical and sociodemographic characteristics may limit the generalizability of the results to more vulnerable preterm infants with diverse backgrounds. Furthermore, while significant improvements were observed, the intervention was limited to a 12-week period and lacked long-term follow-up, which prevents understanding whether these benefits are sustained over time. However, evidence from a single-case study of an infant with hemiparetic cerebral palsy and twin anemia polycythemia sequence reported that developmental gains were sustained or enhanced at a 4-month follow-up, particularly in sensory and motor outcomes (23). Although these findings provide preliminary support for the potential sustainability of HEP Approach intervention effects, further controlled studies with larger sample sizes and longer-term follow-up are necessary. A potential limitation was that, although the researchers did not provide the intervention for the control group, it was conducted by experienced NDT/Bobath trained therapists, and detailed records of the interventions were kept. This ensured consistency in the application and mitigated potential bias, preventing it from being a limitation in the study. In addition, the study did not assess alterations in infants' functional performance or their engagement in daily activities, thus constraining the interpretation of how developmental achievements manifest in everyday contexts. Although the HEP Approach led to significant changes, it was not explicitly designed to target sensory enrichment; therefore, the observed effects may be due to increased movement and exploration rather than the sensory components alone. Nonetheless, this study represents the first RCT to explore the HEP Approach in preterm infants, providing valuable preliminary data. Future research should adopt broader inclusion criteria, including preterm infants with more complex clinical profiles such as high-grade intraventricular hemorrhage or significant sensory impairments, implement an extended follow-up period, and utilize multi-center designs with socioeconomically and culturally diverse samples to enhance the generalizability and validity of findings. Moreover, ecologically valid tools such as Goal Attainment Scaling (GAS), the Canadian Occupational Performance Measure (COPM), or the Young Children's Participation and Environment Measure (YC-PEM) should be considered to assess real-world functional outcomes and participation. In addition, future studies could investigate the feasibility of implementing the HEP Approach in home-based, hybrid or telehealth formats, which may further increase accessibility and applicability across diverse settings.

In conclusion, after 12 weeks of early interventions, significant improvements in motor skills and sensory functions were observed in preterm infants, along with a reduction in caregiver anxiety. The HEP Approach led to superior improvements in fine and gross motor skills, as well as certain sensory functions, compared to the TT intervention. Both the HEP Approach and TT interventions were similarly effective in reducing caregiver anxiety.

These findings underscore the significance of early interventions in promoting both infant development and caregiver well-being. The HEP Approach, in particular, could be integrated into standard care practices for preterm infants, offering a compelling alternative intervention for improving developmental outcomes. This study suggests that the HEP Approach may be a useful EI model for physical and occupational therapists to promote developmental gains and ultimately functional performance in preterm infants. The integration of numerous occupational therapy theories makes this approach uniquely suited to occupational therapists. Future research should focus on examining the long-term effects, sustainability, and broader applicability of these interventions across diverse populations and clinical settings to refine care strategies.