Posture Development from 6 to 14 Months in Infants with Vs. without Risk for ASD

Background: During the first 14 months, TD infants progress from postures in which the body is supported by a surface (lying) to postures that require greater strength, muscle coordination, and balance (unsupported sitting, all fours, standing). Although it is well established that individuals with ASD demonstrate difficulties with postural control (Fournier et al., 2010), relatively little is known about the emergence and course of posture development in infants eventually diagnosed with ASD.

Objectives: 1) Describe trajectories of posture development in infants at heightened ASD risk (later-born siblings of children with ASD; HR) and infants with low ASD risk (infants with a negative family history of ASD; LR); and 2) Evaluate the extent to which delays or impairments predict a later ASD diagnosis at 36 months.

Methods: Twenty-five LR and 59 HR infants were observed at home for 25 minutes at 6, 8, 10, 12, and 14 months. Durations of lying, supported sitting, unsupported sitting, all-4, supported standing, and unsupported standing were coded from 6 to 14 months. At 36 months, HR infants received language and ASD diagnostic evaluations using the ADOS-G (Lord et al., 2000) and Mullen Scales of Early Learning (Mullen, 1995). Fourteen HR infants were diagnosed with ASD (HR-ASD), 17 HR infants were classified as language delayed (HR-LD), and 28 HR infants received no diagnosis (HR-ND). 

Results: Hierarchical Linear Modeling was used to compare posture development across groups. All groups declined in Lying, but the HR-ASD group spent more time than the LR, HR-ND, and HR-LD groups in Lying at 10 (p=.005; .011; .022) and 12 months (p=.011; .030; .045). With regard to Sitting, HR-ASD and HR-LD groups spent more time than the LR group in Supported Sitting (p=.016; .035) and less time in Unsupported Sitting (p=.002; .042) at 6 months. In terms of All-4, the HR-ASD group did not exhibit the decelerating pattern of growth characteristic of the LR, HR-ND, and HR-LD groups (p < .001). The HR-ASD group spent less time in All-4 than LR, HR-ND, and HR-LD groups at 8 (p=.002; .006; 025) and 10 months (p = .009; .038; 017), however, they caught up the other groups by 12 months, and at 14 months spent more time in All-4 than the other three groups (p = .001; .023; 010). For Supported Sitting, the HR-ASD and HR-LD groups exhibited slower growth than the LR group (p=.002; .024), diverging from the LR group by 8 months (p=.001; .009). The HR-ASD group also exhibited slower acceleration than the LR group in Unsupported Standing (p=.005) and spent less time in this posture by 14 months (p=.006).

Conclusions: Relative to LR infants, HR-LD and HR-ASD infants exhibited delays in Unsupported Sitting and Supported Standing. Delays in All-4 were specific to ASD, and from 10 months on, the HR-ASD infants spent more time than all three groups in less developmentally advanced postures (i.e., Lying: 10-12 months and All-4: 14 months). Taken together, these findings indicate that posture delays are likely among the earliest identifiable disruptions in the unfolding of ASD.