Keep in mind, the chart is made in the west by Western doctor. It should suit those who are born from Western parents as far as height is concerned.
So, I don't think you should be worried if your son's height is not as tall as projected in the chart as genetics play a very pivotal role in a person height.
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About Me:
I am a 263 days / 8 months, 3 weeks & 2 days old baby