Dear all:
There was a question on all the exam preps I looked at before taking my first question that always troubled me because I had come from a background using charts to track the growth trajectory (NOT what percentile a baby was).  That question was when the baby doubled their birth weight.  At one point, I did check this out on the old CDC growth charts and the variability was considerable.  I've just done this again for the WHO charts and the variability is less -- probably because they used only breastfed infants and eliminated the overstuffed formula fed babies who grew slowly at first (probably because they were on the starve and stuff method of feeding that doesn't work for a small stomach) and then faster (probably because they had then learned to overeat from the constant stuffing after a period of starvation).  

So, with the new growth charts I have the answer to the question but I'm not sure what is in "the books". 

The range of doubling of birth weight for girls is:
103 days (3.4 mo) at the 1st centile
108 days (3.6 mo) at the 3rd centile
128 days (4.2 mo) at the 97th centile
130 days (4.4 mo) at the 99th centile

The range from the 1st to the 99th centile is 30 days (1.0 mo)


The range of doubling of birth weight for boys is:
83 days (2.7 mo) at the 1st centile
92 days (3.0 mo) at the 3rd centile
125 days (4.1 mo) at the 97th centile
130 days (4.3 mo) at the 99th centile

The range from the 1st to the 99th centile is 47 days (1.5 mo)


So, babies at the top end of the percentile curve double their birth weight more slowly than babies at the bottom end of the curve -- primarily because they are bigger to start with.  To be honest, with a range of a month or more, I cannot see the utility of this "tool".

Best 

Susan Burger, MHS, PhD, IBCLC

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