Dear all:
Sorry, I owe Heather an apology.  I was operating on some old information and the qualitative research done by Magda Sachs a while back where some of the clinics were pushing the 50th percentile of weight for age as normative when it is not.  Glad to know I was wrong.

I would go further than Heather in saying you can't diagnose lactational insufficiency from weight gain at all.  You must investigate the baby's capacity to remove milk before determining that there is any "insufficiency" on the maternal side.  I do agree though that a baby who is incapable of removing sufficient milk to maintain adequate growth may ultimately lead to "insufficiency".


**************
Many thanks to Jacquie Nutt for catching my error - and yes she calculated similar numbers to what I had in my charts!.  I had a bunch of columns and looked at the wrong one for kg.  That was actually my column for determining weight gain over 7 days.  How humiliating!!!   

The grams were in the very first column and I actually derived the ounces from the grams. 

So, to summarize the CORRECT info:

A girl whose weight was at the 3rd percentile at birth and on day 3, 
who gained 1/2 ounce per day from day 3 to 12 weeks of age would be:

904.1 g or 31.8 oz below a girl who grew along the 3rd percentile at 12 weeks of age.


A girl whose weight was at the 3rd percentile on day 14, 
who gained 1/2 ounce per day from day 14 to 12 weeks of age would be:

780.1 g or 27.4 oz below a girl who grew along the 3rd percentile of weight-for-age.


A boy whose weight was at the 3rd percentile at birth and on day 3, 
who gained 1/2 ounce per day from day 3 to 12 weeks of age would be:

1,276.1 g or 44.9 oz below a boy who grew along the 3rd percentile of weight-for-age.


A boy whose weight was at the 3rd percentile of weight-for-age on day 14, 
who gained 1/2 ounce per day from day 14 to 12 weeks of age would be:

1,098.1 g or 38.7 oz below a boy who grew along the 3rd percentile at 12 weeks of age.

****************

And while I didn't do all the calculations, I plugged in the numbers for a baby boy who started at the 3rd percentile of weight-for-age and grew along the 3rd percentile of weight velocity and the difference between the expected weight-for-age if that boy grew along the 3rd percentile curve all the way to 12 weeks.  What I found was

A boy whose weight was at the 3rd percentile of weight-for-age at day 3, 
who gained at the rate of the 3rd percentile of weight velocity (g/ or oz/day) from day 3 to 12 weeks of age would be:

1,160.6 grams or 40.8 oz below a boy who grew along the 3rd percentile of weight-for-age

So, even if I did the other three combos -- it is clear that you cannot treat weight velocity percentiles in the same way that you treat weight-for-age percentiles.  Again, babies were meant to wobble around the curve in a certain range, but not to continue to deviate farther and farther away from their initial curve.   Weight velocity SHOULD by definition wobble around a curve therefore average out to be at the 50th centile. 

*****************

For Teresa:
I absolutely give credence to "catch up" and "catch down" growth which is why I set my "customized curves" where I show the baby's growth along three percentile (or for off the charts babies -- z-score) curves based on where the baby is at around 2 weeks of age -- provided the baby didn't do a steep plummet in those first two weeks.  

Yes, most babies will drop AND also go back up again.  Wobble is normal and perfectly fine.  And that is why the velocity curves are really pretty useless. A normal baby might actually lose weight over short periods and that's fine.  But that same baby will gain more weight at other periods of time.  So, if a baby followed the 3rd percentile of the velocity curve for very long without having some periods of being on the 95th percentile --- that baby would end up being much much lower than the calculations I've shown above. 


So while a slight slip or wobble around the curves is normal, a consistent decline or flatlining in growth is not.  

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