One Side of My Baby's Body Moves Differently
The short answer
Babies should generally use both sides of their body equally. If one side consistently moves differently, is weaker, stiffer, or less coordinated, this warrants evaluation. Asymmetric movement can indicate hemiplegia (cerebral palsy affecting one side), brachial plexus injury, or other neurological conditions that benefit from early therapy.
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By Age
What to expect by age
Some asymmetry in newborns can be positional and resolves over weeks. However, if one arm or leg consistently moves less, is stiffer, or one hand is always fisted while the other is open, mention it to your pediatrician.
By now, both sides should be fairly equal in movement. If your baby reaches with only one arm, or one leg kicks less, evaluation is recommended. Early identification of asymmetry leads to much better outcomes with therapy.
Asymmetric crawling, consistent preference for one hand, or one side seeming weaker should be evaluated. Physical therapy started at this age is very effective.
Asymmetric walking, persistent one-hand preference, or one-sided weakness that affects daily activities should be thoroughly evaluated by a pediatric neurologist.
What Should You Do?
When to take action
- Mild preference for one hand during some activities.
- Both sides can move well even if one is slightly preferred.
- Your baby is over 18 months and developing normal hand preference.
- Consistent weakness or stiffness on one side.
- Strong hand preference before 12 months.
- One hand always fisted while the other is open.
- Sudden weakness on one side (stroke symptoms).
- Progressive loss of movement on one side.
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
Worrying about your baby means you care. That is a good thing.
Related Physical Concerns
My Baby Seems to Use One Side More Than the Other
Babies should use both sides of their body fairly equally during the first 18 months of life. While slight preferences can be normal, a consistent pattern of favoring one side - using one arm much more than the other, crawling with one leg dragging, or turning the head predominantly one way - should always be discussed with your pediatrician. Early identification of asymmetry leads to the best outcomes.
Baby Not Using One Arm or Hand
If your baby consistently avoids using one arm or hand, it deserves evaluation. Before 18 months, babies should use both hands roughly equally - strong hand preference before this age can indicate a concern with the less-used side. Possible causes include brachial plexus injury (Erb's palsy) from birth, nursemaid's elbow, fracture, or neurological differences. Early identification leads to better outcomes with therapy.
My Baby Prefers One Hand Too Early
True hand preference should not develop until at least 18 months to 2 years of age. If your baby consistently uses only one hand and ignores or avoids using the other before 18 months, it may indicate that the less-used hand or arm has reduced strength or coordination. This is different from a slight preference and is worth discussing with your pediatrician.
My Baby Only Army Crawls
Army crawling (also called commando crawling) is a completely valid and normal way for babies to move. Many babies army crawl for weeks or even months before transitioning to hands-and-knees crawling, and some skip hands-and-knees crawling entirely. What matters is that your baby is independently mobile and exploring their environment.
My Baby Crawls Unevenly
While some variation in crawling patterns is normal, consistently favoring one side or dragging one limb while crawling warrants attention. Babies should use both arms and both legs relatively equally when crawling. Persistent asymmetry could indicate muscle tone differences, hip issues, or neurological concerns that benefit from early evaluation.
My Baby Still Has the Fencing Reflex (Persistent ATNR)
The asymmetric tonic neck reflex (ATNR, also called the fencing reflex) causes your baby to extend the arm on the side they are looking toward. It should integrate between 4-6 months. If the ATNR persists strongly beyond 6 months, it can interfere with bringing hands to midline, bilateral hand use, and rolling. Evaluation is recommended.