Ultrasonographic evaluation of suprahyoid muscle thickness during the transition to full oral feeding in preterm infants

The transition to full oral feeding (FOF) is a critical milestone for discharge in preterm infants and reflects the maturation of multiple physiological systems, particularly swallowing-related neuromuscular coordination. Suprahyoid muscles play a key role in swallowing by enabling elevation of the hyoid–laryngeal complex and protecting the airway. However, the relationship between the structural development of these muscles and the achievement of oral feeding in preterm infants remains insufficiently explored. This prospective single-center observational study included 28 preterm infants born at ≤ 32 weeks of gestation. Suprahyoid muscle thickness (right and left digastric, right and left mylohyoid, and geniohyoid muscles) was measured by ultrasonography at two time points: within the first 72 h of postnatal life and at the time of full oral feeding. Somatic growth parameters, including body weight, body length, and head circumference, were recorded simultaneously. Changes in muscle thickness over time, correlations with somatic growth parameters, and the predictive value of early muscle thickness for time to achieve FOF were analyzed. All suprahyoid muscle thicknesses increased significantly between the early postnatal period and the time of FOF (all p < 0.001). At the time of FOF, digastric muscle thickness ranged approximately between 2.7 and 3.2 mm, mylohyoid muscle thickness between 1.6 and 2.0 mm, and geniohyoid muscle thickness between 3.0 and 3.6 mm, with values appearing to cluster within a relatively narrow range during successful transition to oral feeding. A positive correlation was observed between body weight and certain muscle thickness measurements, particularly left mylohyoid (r = 0.453, p = 0.015) and right digastric muscles (r = 0.386, p = 0.043). However, suprahyoid muscle thickness measured within the first 72 h did not independently predict the time required to achieve FOF in multivariable regression analysis. Conclusion: Suprahyoid muscle thickness increases significantly during the transition from early postnatal life to full oral feeding in preterm infants and appears to cluster within a relatively narrow range at the time of feeding maturation. Ultrasonographic evaluation of suprahyoid muscles may provide a non-invasive approach to describe structural changes associated with feeding maturation in preterm infants. (Table presented.)