Newborn Weight Loss Calculation

Updated April 17, 2017

Breast-fed newborn babies may lose up to 10 per cent of their birth weight in the first week of life without cause for alarm or medical intervention; however if they lose more than 7 per cent in the first 72 hours, the breastfeeding method should be observed by a trained professional. The weight loss calculation is usually performed by a doctor or nurse about one week after birth. Formula fed infants typically lose 5 per cent of their birth weight in the first week. There are multiple explanations for why a newborn might lose weight.

General Conditions

The most common theories about newborn weight loss are: babies are born with extra weight to help with the stress caused by labour and the transition to life outside the womb; and for a breast-fed baby, his mother's milk does not come in fully for three to five days. Some women mistakenly give up breastfeeding before their milk has come in, concerned that their baby is not gaining weight. However, breastfed babies are receiving colostrum, which contains all essential nutrients but comes in small quantities. Lactation consultants or breastfeeding education classes before birth can help to counteract this trend.

Special Conditions

The use of intravenous (I.V.) fluids in labour causes a large shift of fluid from the mother to the foetus. Therefore, the newborn infant's initial weight loss may be greater than 10 per cent maximum due to surplus fluid loss. Dry heat from radiant warmers and incubators can also cause excessive fluid loss for a newborn if he is left there for a long period. Lastly, giving newborn babies water or formula can also contribute to weight loss.

Steps to Ensure Accurate Weight Loss Calculation

A trained medical professional such as a doctor or nurse usually weighs the infant before he leaves the hospital and about one week after birth. The scale should be balanced and the newborn's clothes and diaper removed. The calculation performed is birth weight ,less current weight = difference, then difference divided by birth weight to derive percentage weight change. Depending on the results, such as a breast fed baby losing more than 10 per cent of his birth weight, the paediatrician's attention may be required. However, most babies will regain their birth weight within two to three weeks and their initial weight loss will be within the normal range.

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About the Author

Lea Webb is a CPA and internal auditor with the State of California. She holds degrees in politics and public administration. She has written professionally as communications coordinator for a member association and as a government performance auditor.