Sunday, March 21, 2010
How Handedness Develops in Infants
by Robert Needlman, M.D., F.A.A.P.
reviewed by Robert Needlman, M.D., F.A.A.P.
When doctors examine newborns, they check to make sure that the baby's left and right sides are the same. It's especially important that the baby moves her arms and legs equally on both sides. If one side doesn't move as well as the other, or if the reflexes are much stronger on one side or the other, it could be a sign that the brain did not form normally or that there was damage to the brain either before or during the birthing process. So, it's important that newborn infants do not show a strong preference for their right or left hand.
However, it is not uncommon (nor is it necessarily concerning) for observant parents to notice that their infants tend to hold one hand more fisted than the other, wave one arm more vigorously, or lie with their head turned to one side more than the other. (Some infants develop a tightening of the neck muscles that forces them to look to one side, a condition called torticollis; this has nothing to do with handedness, however.)
Which hand does your baby reach with?
When researchers study babies, they, too, notice that their movements are not completely equal from side to side. A greater percentage of infants--60 to 70 percent--turn their heads to the right more of the time. Those who turn to the left are somewhat more likely to grow up as left-handers.
At four to six months, more of them hold a rattle for longer in their right hands than in their left. And sometime between six and nine months, most begin to show a clear preference for reaching for a toy with their right hand, regardless of whether the toy is placed on the right or left sides. What's interesting, though, is that while infants seem to prefer one side to another, they are not absolute about it. They also use the nonpreferred side a fair amount of the time.
Between 12 and 18 months, most infants are able to hold a toy in one hand and move parts of the toy around with the other. Most (about 70 percent) hold the toy in their left hand and manipulate it with their right (the manipulation being the more coordinated, complex movement). About one in seven manipulate with the left, and about the same number don't show a clear preference.
Greater muscle control leads to a clearer preference
After 18 months, children do more and more make-believe play, and their hand movements become more and more complex. At the same time, the stability of hand preference increases--in the sense that children use their preferred side more consistently over their nonpreferred one--and the number of children who don't seem to have a hand preference goes down.
By age three or four, most children are doing a lot more complex fine-motor activities, such as drawing and writing, stringing beads, and cutting with scissors, so that their handedness becomes much more evident. A four-year-old who has not yet shown a hand preference may have less mature muscle control and coordination generally.
Both hands used for most things in early years
As you watch your infant, you might notice that she tends to lie with her head to one particular side or look at one hand more than the other. It's only a cause for concern if you notice that she only uses one side, or if one side moves much less or seems much weaker than the other. Through the first three or four years, your child will probably use both hands for most things, such as picking things up, throwing, and stacking, but you may notice a preference for one side or the other that seems to grow stronger over time. An early preference for the left doesn't mean that your child will necessarily end up left-handed, however. Hand choice usually isn't reliable and stable until after age four.
When to consult a healthcare professional
If your child isn't showing any hand preference by age three or four, it may be a sign of delayed maturation. In most cases, children catch up later on their own, following their own developmental timetable. In other cases, children benefit from work with an occupational therapist, who can help build coordination and confidence. If you have concerns (for example, your preschool-age child is having trouble with cutting or holding a crayon or pencil), it's wise to speak with your child's healthcare provider and consider arranging an assessment by an occupational therapist.
Credits to Chin Yee Jah, T5
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