Perinatal stroke causes abnormal trajectory and laterality in reaching during early infancy.

Doctors filmed 14 babies who had a stroke around birth. They also filmed 14 babies with no brain injury. All babies were 2 to 7 months old. The team tracked how each arm moved when the baby tried to touch a toy.

Stroke babies reached in a straight, stiff line. They used one arm much more than the other. Healthy babies used curved paths and both arms evenly. These differences showed up before most parents notice anything wrong.

Eklöf et al. (2019) looked at brain scans, not arm moves. They saw that extremely pre-term babies later diagnosed with ASD had less brain asymmetry. The two studies seem opposite, but they measure different things: one looks at arm use, the other at brain shape. The babies are also different: stroke versus pre-term.

Yaari et al. (2018) tracked Bayley scores in pre-term infants. They found that the gap between pre-term and full-term babies keeps growing. Chao-Ying shows the same widening gap, but only for reaching after stroke. Together they tell us that early curves matter for every high-risk group.

Kuang et al. (2025) took the idea further. They used Bayley trajectories to predict which very pre-term babies would later get an ASD label. Their model works like Chao-Ying’s arm test: catch the odd curve early, act sooner.

You can spot stroke damage in the first half-year by watching how a baby reaches for your finger or a rattle. If the path is ruler-straight or one arm stays still, refer to early-intervention physiotherapy right away. No special gear is needed—just a toy and your eyes.