PMAPostmenstrual age AIM The aim of this study was to investigate the relationship between the characteristics of spontaneous movements in preterm infants at term age and developmental delay at 3 years of age.METHOD We analysed video recordings of the spontaneous movements in the supine position of 124 preterm infants (44 males, 80 females) at 36 to 44 weeks postmenstrual age (PMA). The infants were born preterm (22-36wks PMA; birthweight 489-1696g) and had not received a diagnosis of a neurological or developmental disorder by the age of 3 years. The recorded spontaneous movements were quantified using six movement indices, which were calculated from two-dimensional trajectories of all limbs. The infants were divided into three developmental groups, normal, borderline, or delayed, based on their developmental quotient as calculated using the Kyoto Scale of Psychological Development 2001 (Kyoto Scale) at 3 years of age. Group differences in the movement indices were analysed. RESULTSIn the delayed group, average velocity of arms and legs were significantly lower (p<0.05 and p<0.01 respectively), the numbers of movement units of arms and legs were significantly lower (p<0.05 and p<0.01 respectively), kurtosis of acceleration of arms and legs was significantly higher (p<0.05 in each case), and correlation between limb velocities was higher (p<0.05) than in the normal group.

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In the field of motor development, a question exists whether spontaneous activity in early infancy serves as a precursor to later-emerging goal-directed behaviors. To answer this question, it is necessary to investigate in detail the properties of spontaneous movements in individual infants. In the current study, we longitudinally examined the spontaneous movements of the end points of the limbs in 6 infants aged 2-4 months. Examinations were carried out every week by using a motion analysis system, and the number of recordings performed for each infant varied from 6 to 9 times. Our major finding was that there was an age-related increase in the velocity and position correlation between arms and between legs, whereas there was no significant change in the velocity, duration, and amplitude of movements of individual limbs. That is, the pattern of spontaneous movements changes from a general activity involving all the limbs to an activity involving more selective interlimb coordination from 2 to 4 months of age. These findings suggest that the dissociated movements of a selective combination of arms or legs during spontaneous movements may be a precursor to functionally dissociated movements during goal-directed behaviors.