Newborn weight loss in the first few days of life is a common occurrence. However, it's crucial to monitor this weight loss to ensure the baby is receiving adequate nutrition and to prevent potential complications. Knowing how to calculate your newborn’s percent weight loss is critical to ensuring adequate feeding. This article provides a detailed guide on infant weight loss calculation, its significance, and related factors.
Why Monitoring Weight Loss Matters
Protecting a newborn baby from excessive weight loss is one of the most important ways we can protect their health and brain. Excessive weight loss can result in conditions such as dehydration, low blood sugar (hypoglycemia), excessive jaundice (hyperbilirubinemia) and even hypernatremia (severe dehydration) all of which can negatively affect a child’s brain development.
The American Academy of Pediatrics recommends no greater than 7% weight loss for all newborns. Newborns who lose greater than 7% are at highest risk for developing hyperbilirubinemia and hypernatremia.
The Infant Weight Loss Calculation Formula
The first step is to know your baby’s birth weight in grams (g), not pounds and ounces. To calculate the percentage of weight loss, you'll need the baby's birth weight and their current weight, both measured in grams. Here's the step-by-step formula:
Step 1: Determine the Weight Difference
Subtract the baby's current weight from their birth weight.
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Weight Difference (g) = Birth Weight (g) - Current Weight (g)
For example, If the birth weight is 3340 g and weight at 24 hours is 3127 g:
3340 g - 3127 g = 213 g
Step 2: Calculate the Proportion of Weight Loss
Divide the weight difference by the birth weight.
Proportion of Weight Loss = Weight Difference (g) ÷ Birth Weight (g)
Using the previous result:
213 g ÷ 3340 g (birth weight) = 0.0638
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Step 3: Express as a Percentage
Multiply the proportion by 100 to express the weight loss as a percentage.
Percentage of Weight Loss = Proportion of Weight Loss x 100%
Continuing the calculation:
- 0638 x 100% = 6.38 % weight loss at 24 hours
Alternatively, you can use online tools like the Newborn Weight Loss Tool (NEWT) to enter your baby’s birth weight and any subsequent weights along with the date and times they were measured to assess your baby’s nutrition.
Interpreting the Results
In the example above, a weight loss of 6.38% at 24 hours is between the 75th and 90th percentile on the NEWT.
Generally, a weight loss of up to 7% is considered normal. The American Academy of Pediatrics recommends no greater than 7% weight loss for all newborns. Weight loss of ≥10% may be especially detrimental to maternal breastfeeding confidence because such weight loss is associated with increased risk of hypernatremic dehydration and may result in clinician recommendation of either formula supplementation or additional clinical testing.
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Factors Influencing Weight Loss
Several factors can influence a newborn's weight loss, including:
- Feeding Method: Breastfed infants may experience a slightly greater weight loss compared to formula-fed infants.
- Delivery Method: Weight loss at <24 hours was associated with in-hospital weight loss ≥10% after adjusting for clinical predictors and to assess whether 24-hour weight loss predicted whether or not there was a subsequent recorded weight, after adjusting for other clinical predictors.
- Gestational Age: The mean gestation of the infants was 38.2 weeks (SD 1.2 weeks; range 37.0 - 42.6 weeks) and 241/466 (51.7%) of the infants were male.
- Birth Weight: Of all the infants included in this study the mean birth weight was 2.95 kg (SD 0.47 kg), 103/466 (22.1%) had a birth weight of less than 2.50 kg (low birth weight, LBW) and 74/466 (15.9%) were SGA.
- Time of First Weighing: Because time of birth may have affected whether an infant is reweighed at <24 hours, we conducted sensitivity analysis examining the above outcomes for weights measured at <30 hours and <36 hours.
Weight Loss Patterns
Studies performed in developed countries quote a weight loss of between 4 - 7% in the first days of life. In a study, the maximum weight lost was 4.4% (95% CI 4.1 - 4.6%), which occurred on day three. Infants started to gain weight between days three and four with a mean gain of 13 g/kg/day (95% CI 9 - 17 g/kg/day). Weight gain subsequently continued until day seven.
Implications of Excessive Weight Loss
Excessive weight loss can lead to several complications:
- Dehydration: Weight loss of greater than 10% has been associated with dehydration and hypernatremia.
- Hypoglycemia: It has been shown that around 20% of all newborns develop hypoglycemia that can negatively affect brain development by 3 hours of life.
- Hyperbilirubinemia: It has been shown that newborns who lose greater than 7% are at highest risk for developing hyperbilirubinemia and hypernatremia.
- Hypernatremia: Weight loss of greater than 10% has been associated with dehydration and hypernatremia.
- Reduced Breastfeeding Confidence: Weight loss of ≥10% may be especially detrimental to maternal breastfeeding confidence because such weight loss is associated with increased risk of hypernatremic dehydration and may result in clinician recommendation of either formula supplementation or additional clinical testing.
Predicting Subsequent Weight Loss
First-day weight loss is routinely measured for newborns, but no studies have examined whether greater weight loss in the first day predicts subsequent weight loss. Infants losing ≥4.5% birth weight at <24 hours had greater risk of eventual in-hospital weight loss ≥10% (adjusted odds ratio 3.57 [1.75, 7.28]). Among breastfed infants, each additional percentage weight loss by 24 hours was associated with an odds ratio (OR) of 1.47 (1.23, 1.74) for eventual in-hospital weight loss ≥10%.
Monitoring and Intervention
The most important ways we know that a child is receiving enough milk is by closely monitoring weight loss, preventing excessive weight loss, monitoring for hyperbilirubinemia, hypoglycemia and dehydration and ensuring that a newborn is satisfied by their feedings. If your newborn develops signs of hunger as listed on our HUNGRY flyer, please get immediate medical attention. If medical attention is not available and your child appears to not be receiving sufficient milk, please supplement first then seek evaluation from a pediatrician or other physician or nurse practitioner trained in newborn care.
Breastfeeding and Weight Loss
Exclusive breastfeeding reduces infant infectious disease. Breastfeeding protects against gastroenteritis, lower respiratory infection, and other infectious diseases in infancy. Longer duration of exclusive breastfeeding is associated with greater benefit. Low breastfeeding confidence in the first week of life predicts early breastfeeding discontinuation, and poor infant weight gain has been associated with reduced breastfeeding confidence.
Study on Weight Loss
A retrospective cohort design study of 1,049 infants born between June 2007 and February 2008 at the University of California, San Francisco who received Level 1 care only was conducted. Data on gestational age, birth weight, gender, delivery method, feeding type (breast, formula, or both), and all recorded infant weights was extracted.
The results showed that mean age at in-hospital weight nadir was 38.7 ± 18.5 hours. Among 150 infants who had lost 4.5% of birth weight by 24 hours, 16 (10.7%) eventually were documented as losing ≥10% birth weight, whereas only 24 (4.3%) of the 568 infants who did not lose 4.5% birth weight by 24 hours eventually were documented as losing ≥10% birth weight (p = 0.002).
Weight Gain After Initial Loss
Infants started to gain weight between days three and four with a mean gain of 13 g/kg/day (95% CI 9 - 17 g/kg/day). Weight gain subsequently continued until day seven. From day two until day six there was no significant difference between the weight gain velocity between boys and girls. However on day seven girls had a significantly greater weight gain than boys (20 g/kg/day vs.
Weight Loss in Developing Countries
In a study in Maela Camp for displaced persons, a healthy term breast fed infant born in the tropics, loses no more than five per cent body weight after birth, with the maximal loss on day three, and regains birth weight by day six of life. Our study demonstrated no difference between normal weight, low birth weight and SGA infants. After day three, infants gained weight, having a weight velocity of between 13 - 18 g/kg/day (95% CI 10 - 20 g/kg/day).
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