Dear all:

I can't even count the number of maternal and child nutrition and anthropometry courses 
I have sat through.  NEVER until I became a lactation consultant did I hear of the rule of 
doubling and tripling the weight as a rule of thumb.

There are very serious problems with this approach. 

First, there is the mere statistical problem of regression to the mean.  With any 
measurement we take, whether it is a clinical observation, mechanical measurement, or 
biochemical value --- there is measurement error.  This means that any value can be 
high or low and for babies who are weighed at birth, some of the very high and very low 
values are due to measurement error.  At the next measurement is it highly unlikely that 
the measurement error will be in the same direction.  So there is a greater chance that 
the value will be higher if the value was low, or lower if the value was high at the next 
measurement.  This is known as regression to the mean.

Second, if there was a problem in utero that caused that baby to grow at higher or lower 
than the rate that that baby should have grown, it may be corrected in the extrauterine 
environment.  A baby that was growth retarded because of poor placental growth may 
flourish once it gets breast milk.  A baby that had macrosomia because of gestational 
diabetes may then be able to grow and a slower and healthier rate.  So, again this 
contributes to APPARENT "catch up" and "catch down" growth.

Third, birth weight is not predictive of future size --- so the genetic factor (which is 
MINIMAL on a POPULATION basis --- all ethnicities grow at a very similar rate when they 
have good nutrition) on an INDIVIDUAL basis can kick in and if the baby is fed according 
to cues should grow more at the genetically determined rate.

Fourth, when a baby slows down in growth --- whatever happened early on when the 
baby was growing according to a chart may no longer be relevant.  It does NOT help the 
problem solving of whether or not the baby is growing at a healthy rate or not.  

Really, a doubling or tripling is even more crude than what was LONG AGO discarded in 
international nutrition circles.  We used to use percentages, percentiles and z-scores of 
average values.  That does not work on an individual basis and should NEVER be used for 
diagnostic purposes.  Using some statistical method based on average weight is only 
marginally useful on a population basis to figure out if a nutrition program had an impact.

The pattern of growth is but a clue to investigate further.  The far more important factor 
is how you investigate into both the infant's and maternal behavior and developmental 
milestones.  Every now and again you get a zebra of some hormonal factor such as 
changes in mom's thyroid level or something rare that was never diagnosed in the infant.  

I have to say that I was shocked that these type of questions were used on the IBCLE 
exam.  And I would probably still fail those questions because I still think the doubling or 
tripling time is NOT what we should be evaluating.

Best, Susan 

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