Dear all:

Blanket statements with vague references such as "As for the usefulness of test weighing in general, I have read several times, from several sources that anything from 'at least' 24 hours or '2-5 days' of weighing is needed for reliable intake information, because babies take different amounts at different times of day (as do all human beings)"  do not get to the heart of the whys and hows to use indicators appropriately.  And in fact, I would really like to see the original full articles to support this statement since I have not come across such blanket statements in the extensive literature search that I did.  Furthermore, the statement that "I think mothers are at least as interested as researchers in accurate results." is not the point. Researchers and mothers are asking entirely different questions.  What is needed to answer a specific research question may be entirely different than what a mother needs to know to take the appropriate steps so that she breastfeeds with confidence.

Reliability is comprised of two different elements -- the precision of the measurement instrument and the dependability of that indicator over time.  You can have a very precise instrument such as the creamatocrit which will give you very similar readings from aliquots of the same sample of milk.  Yet if you measure different samples from the same woman at the beginning of the feed or the end of the feed, at different times of the day, from different breasts, you will get hugely different readings.  In some cases such has height, you can control for dependability.  It is known that you shrink in height over the course of the day.  So if you measure someone's height at the same time of the day, you will get more similar readings than if you measure that person's height in the morning and in the evening.

There are many many measurements that have issues where one has to take into account dependability.  One of these is prolactin.  We know that it spikes and then declines.  We know (Hale did a nice presentation on this) that the RESTING prolactin levels are important, not the peaks.  You do NOT have to take continual measurements of prolactin over 24 hours even though I would say that its "dependability" is far less than feed to feed variability of infant intakes.  You do the measurement after the period of time when it returns to the resting levels (I'd have to look it up but I have a vague memory that it may be around 90 minutes).  

Similarly, blood pressure will go up and down.  Perhaps it may be done, but I have never known someone to where a blood pressure cuff for 24 hours.  Instead, a good clinician would ask you relevant questions that might reveal such relevant items as whether you sucked down three Venti Lattes or just came from your Martial Arts class or are completely stressed out about the fact you just lost your job that day before your blood pressure was taken.  

Now, in some cases, for less common events, like a heart arrhythmia, it may make sense to have a monitor to capture that rare event.

In terms of infant feeding, the body of literature I found shows that in developing areas of the world, the intake of babies around the clock actually is fairly even.  So much so that you can get a reasonable estimate of intake by averaging one or a few measurements from pre and post feeding weights and multiplying by the number of feeds.  In developing areas of the world, we often have a pattern whereby babies are forced into eating more during the daylight hours.  In this case, if you know the pattern of eating, you can make reasonable estimations on a population basis for some research purposes if you have a smaller subset of data that shed more light on that pattern of eating.

Furthermore, having spent a lot of time having to study all sorts of other dietary intake estimation methods, we know for a fact that repetitive long term measurements change eating and feeding behavior in ways that a one time or infrequent measurement may not.  Someone who has to weigh every bit of food before eating it and then measure the plate waste (the food leftover) actually does change their eating patterns.  In some cases, simple food frequency methods can get at useful information much more reliability than the supposedly more accurate weighing methods.  For instance, you can, on a community level, get a better sense of the intake of vitamin A rich foods for planning community level dietary interventions by asking about the frequency of consumption of certain key foods.  Coupled with other indicators such as taking retinol levels on a small representative sample of the population you can design a very good tracking system for whether or not your dietary interventions are changing both practice and outcome.  

In terms of mothers, what they really need to know can be categorized as the following:

1) whether or not their babies are doing fine with the current pattern of feeding from the breast (e.g time and duration)
2) whether interventions (tongue exercises, tubes on the breast, nipple shields, pumping etc) are actually assisting the baby to get more from the breast
3) whether they can safely reduce supplementation with breastmilk substitutes that may have been prescribed by a health care practitioner

With all my training in epidemiology, anthropometry and measurement issue, I would argue that it would be ludicrous to claim that you need to conduct test weighing for 24 hours to make reasonable decisions about such issues, let alone for 3-5 days.  I'd say that test weighing is probably more useful for 2) than for 1) and 3).  I'd say that you need to see the mother and baby more than once for all of these issues. And I'd say the pre and post feeding weighing is useless without a thorough history of the feeding patterns and behavior.  In most cases, I find that mothers are quite reassured about 1) when they see that their baby is actually drinking far more milk than they ever really imagined.  In some cases, I have used the scale to convince mothers that dropping feedings according to the new trend of training 8 week olds to sleep 12 hours a night vociferously endorsed by a growing pediatric practice is NOT going to permit their baby to drink a sufficient amount of milk to gain appropriately (and thereby stave off a few of the iatrogenically induced cases of failure to thrive).  

In fact, in the one case of the baby that was drinking huge amounts of milk from the breast but still losing weight -- I figured it out in one pre and post feeding test weigh.  The only purpose of a 24 hour pre and post feeding test weigh in that case would have been to convince the pediatrician, but she was so convinced the mother had low supply that it took the much more open minded endocrinologist who diagnosed the condition to convince the pediatrician otherwise.  

Sincerely,

Susan E. Burger


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