Test weighing

In the 1950s, during the era of the ‘scientification of motherhood’, it was common for babies in developed countries to be weighed before and after a feed, known as test weighing. This practice should not now routinely practiced for term infants because of its lack of precision as a measure of breast milk production.

Test weighing has been referred to at times as "objective measure of milk transfer" – but this is a false statement. No single indicator of milk transfer is objective. Assessment concerning milk transfer requires context.

The density of milk is 0.03g/ml, so in test weighing, grams are expressed in mls.

As health professionals, we can significantly worsen our own and the parents’ anxiety about a baby’s weight by pre- and post-feeds test weighing. Single feed test weighs are dangerously unhelpful for breastfeeding, since any one feed is not indicative of average milk transfers overall, given how variable each breastfeed is.

When I have serious weight gain concerns, that we need to turn around quickly if we are to hold off from formula, then I will ask the parents to come back for a weigh within two or three days, sometimes even the following day if that’s called for.

Test weighing a feed and then measuring the amount of milk (‘residual pumping’) that can be pumped after the baby has finished breastfeeding is also remarkably unhelpful, and should never be used. Even women with very generous supplies may not be able to pump much milk.

I don’t recommend parents use baby-scales to track their baby’s weight at home, but that they allow a provider to do this instead. We need to bear in mind that baby-scales can be calibrated differently, and that it is normal for a baby to gain very little one week, and then quite a lot the next (providing we are not dealing with a premmie or a baby in a vulnerable situation). It is the trajectory over time, on the WHO percentile lines, that matters. If we weigh our babies too much, whether as health professionals or parents, we risk unnecessary worrying and unnecessary formula supplementation.

What is 24-hour test weighing?

Twenty-four hour test weighing is used in research as an indicator of overall breastmilk transfer (taking into account other milk administered other than from the breast), and the parents don’t need to undress the baby, just weigh before and after. But this is only useful using expensive clinical scales, and can nevertheless be disruptive for the baby before and after feeds, especially the baby is already dialled up.

Even in this research setting, milk production with 24 hour test weighing may be underestimated by an average of 10% (range 3-55%) due to infant insensible water loss. Given that the upper end of the range of underestimation is 55%, this variability is significant.

Some clinicians also send parents home with scales, requesting a 24-hour test weigh. I have the view that this can be very disruptive for families, and doesn't yield any more information than careful history-taking and clinical assessment yields. Even though the baby is weighed before and after the feed fully clothed, the use of 24-hour test weighing may reinforce unhelpful infantcare behaviours because test weighing in the 24 hour context

• Rouses infants after a breastfeed, interrupting easy sleep

• Assumes that each infant breastfeed is a 'meal'

• May elevate parental anxiety over how much milk is actually transferred each feed

• Potentially sets up a miserable day for that mother, who needs to stay at home for the test weigh, which may dial the baby up due to decreased sensory motor stimulation.