Growth charts that your doctor uses represent the average weight,
height, or head size of a bunch of normal children. So, your child
is being compared to the national averages of other children in
their age group.
On the growth charts you will see the
percentile lines running parallel to each other. If a child's
weight is at the 50th percentile line, that means that out of 100
normal children his or her age, 50 will be bigger and 50 smaller
(i.e. he/she is falling right in the middle). Likewise the 86th
percentile means your child is bigger than 86 and smaller than
only 14, compared with 100 children his age. There are separate
charts for weight, height, and head circumference.
To see if your child is too skinny or overweight, there is a
'weight for height' chart or a BMI index, which tells you what
percentile the weight is for a child who is that particular
height. Decreasing percentiles in this area is often the first
sign that a child is taking insufficient calories. Depending on
the extent of the poor caloric intake, the child could begin to
get stunted -- the height begins to fall off the growth chart.
Lastly, and this takes a long time to happen, the head growth
slows down, indicating not enough calories for the brain to grow
at a normal rate.
The growth percentiles by themselves don't say much. What really
matters is the velocity of growth. A normal velocity
of growth means the child's growth points will closely parallel
the percentile line above it on the chart. They usually don't worry
about insufficient (or excessive) growth until a child's growth
velocity has crossed at least two percentile lines (e.g., from
above the 90th to below the 50th percentile).
Additionally, if a child's weight, height, or head size is below
the 5th percentile, we might also call them small for age. In that
case, what's most important is to see if the growth points
parallel the 5th percentile line (meaning growth velocity is
normal) or if the child is falling further behind (which is more
concerning). Anything under the 3rd percentile line in
children under 2 years is generally considered failure to thrive
and is cause for concern.
Some parents obsessively follow the growth curves and worry
unnecessarily about insignificant deviations from that perfect
line on the chart. Try to remember that all kids are different and
the charts and percentiles are used as a guideline only.
Does your child appear otherwise happy and healthy? Is she making
nice developmental progress? Is she taking in at least some
protein (milk, yogurt, eggs, meat)? If yes, to any of the
above questions, you likely don't have much cause for concern.
At any rate, you can use the following growth percentile
calculators to check your baby or child's growth. Use the one on
the left for infants (babies under 2) and the one on the right for
children (kids over 24 months).
Infant Growth Percentile Calculator
Child Growth Percentile Calculator