I've read with interest much of the recent disc about before and
after
weights (AC/PC) or test weights (I think it's all the same).  IMO
it's
*one* piece of data, sometimes very valuable, sometimes not much
help, never the whole picture.  I've been changing my opinion about
their usefulness pretty regularly over the past few years.  At first
I
was opposed because of the possible negative impact on mom...
and I was convinced a skilled observer could tell as much....
then attended a research conference and talked with Paula Meier
about premie issues about 1992.  She was working with an experienced
IBCLC and they told about clinical comparisons of the LC's guess and
test weights (as well as how they verified the validity of test wts.
to
accurately reflect vol of intake--double blinded with known vol by
bottle).
The LC reported she was most surprised about the results--about 50%
accuracy.  SO....since then I've seen them used poorly in some
settings/by some health care workers...and well in many settings
by skilled LCs.  However, they do only reflect VOLUME.  That can
be a very useful piece of information in trying to sort out what's
going on.
Used well, it can be very helpful for mom to know whether/how much
suppplement is needed in sick/premie/FTT babies.  There's usually a
lot of work that has gone on first re ways to help baby and support
mom's supply.  Through observation and output, we can add additional
bits of information---then try to put ALL the puzzle pieces together.

*** The real proof of course is in the baby's weight gain.  ***
Even when we know the exact cal content and vol of intake there is
still a *range* of intake needed to acheive WNL *range* of acceptable

wt gain for an *individual* baby!
Equipment and procedure for AC/PC weighing is very importance.  Of
utmost
importance is how it's used/presented/handled.  We need all kinds of
tools.
Good ref: Meier, PP, Lysakowski, Engstrom, Kavanaugh & Mangurten
(1990). The accuracy of test-weighing for preterm infants. J of
Pediatric Gastroenterology and Nutrition 10, 62-65.
My .02--Phyl