Movement smoothness at term-equivalent age is associated with motor developmental delay in preterm infants.

This prospective longitudinal cohort study aimed to quantify limb-movement smoothness at term-equivalent age and investigate whether limb-movement smoothness is associated with motor developmental delay (MDD) in very-preterm or very-low-birth-weight infants. Video recordings of limb movements were obtained at term-equivalent age, and the Bayley Scales of Infant and Toddler Development, Third Edition, was conducted at nine months of corrected age. Upper and lower limb movement smoothness was quantified using a pretrained 2D pose estimator and smoothness indices measured by log dimensionless jerk (LDJ) and spectral arc length (SPARC), with lower LDJ magnitude and less-negative SPARC indicating smoother movement. The quantified movement smoothness was compared between infants with and without MDD. Among 111 infants, 11 (9.9%) exhibited MDD. The LDJ measurements showed significant differences at the right shoulder, elbow, hip, knee, and left elbow between infants with and without MDD (p < 0.05, d ≈ 0.96-1.12). The SPARC measurements showed significant differences at the right shoulder, hip, knee, and left knee between the two groups (p < 0.05, d ≈ 0.64-0.89). The motor composite scores showed significant positive correlations with the absolute values of LDJ and SPARC at the multiple joints. Limb-movement smoothness at term-equivalent age is associated with MDD in very-preterm or very-low-birth-weight infants. Smoothness indices of limb movements can be potentially useful for the early detection of MDD.