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Test weighing (weighing before and after feeding) is the easiest method to assess milk intake in breast fed infants. 1- 3 This method is commonly used during the first weeks of life, during the build-up phase of breast feeding and when newborn infants are ill, both at home and in hospital. 3, 4 It is assumed that the increase in the baby's weight after feeding (in grams) reflects the amount of milk (in millilitres) drunk by the infant. 3 The World Health Organization considers test weighing to be a useful method of assessing milk intake in breast fed infants. 5 This is based on several studies that examined the reliability of test weighing in bottle fed infants, comparing the difference in weight with the amount of milk drunk from the bottle. 1- 4, 6, 7, 8, 9, 10 In these studies, conclusions were based on highly significant correlations between weight change and milk intake, which indicate association but not necessarily agreement between two methods. 11 In particular, a strong association does not exclude poor accuracy or precision. Accuracy is defined as the ability of a measurement technique to measure the true value of a property. Lack of accuracy means systematic error. It has been shown that test weighing is slightly inaccurate because of evaporative water loss (EWL), but this inaccuracy is too small to be clinically relevant. 1, 7 Precision, on the other hand, is related to the spread of results obtained with repeated measurements. If a procedure such as test weighing is imprecise, its clinical usefulness is hampered considerably. We therefore designed a study to assess the accuracy and precision of test weighing in a clinical setting.
METHODS
We studied 100 infants, fed by bottle, cup, or nasogastric tube, admitted to the newborn and infant ward of the Princess Amalia Children's Clinic in a large district general hospital in the Netherlands. Critically ill or haemodynamically unstable patients were excluded. Each infant took part in the study only once. Babies were weighed three times: before feeding, immediately after feeding, and 15 minutes later. Study measurements were made under conditions that reflected regular clinical procedures as closely as possible. Each weight measurement was made with the baby fully dressed, wearing a nappy, and, if applicable,...