Newborn weight gain: what's normal & when to worry

What is it that makes a baby’s weight loss (and gain) so important? At birth, it’s often the second question new parents ask their doctor or midwife once the baby arrives. Is my baby okay? How much does she weigh? During health care visits, it tends to be the first item checked, and the result met with relief or concern.

Perhaps it’s the baby’s inability to communicate whether she is getting enough to eat. Babies do communicate hunger or satiety, but the signs can be subtle. Whatever the reason, weight measurements are viewed by parents and health professionals alike as an indicator of whether babies are getting enough to eat. Knowing how much weight breastfed babies lose in the first days after birth and how quickly lost weight is regained can reassure anxious parents and alert clinicians if there is a need for additional follow-up.

How much weight healthy, exclusively breastfed babies lose in the first days after birth has been the subject of numerous studies including a 2008 literature review in which the authors cited a number of problems with assessing the research: a lack of consistent terminology (day 0, day 1, exclusive breastfeeding); lack of consistent measurements (weights recorded for some but not all days); and, the use of convenience samples (readily available babies) rather than random samples. 

These flaws caused the reviewers to conclude that there was insufficient data to answer the question: How much weight do exclusively breastfed babies lose and then gain in their first 14 days? Like most baby-related measurements, there is no one size fits all. In fact, assigning an absolute number (3, 5, 7 or 10 percent weight loss) is deceptive because it fails to take into account the wide range of birth situations. For example, a 2011 study of the relationship between IV fluids during labor and childbirth and weight change in breastfed babies found that administration of fluids can artificially inflate babies’ birth weight. Rather than using that as the baseline from which to calculate percent-change, the researchers recommended relying upon babies’ weight at 24 hours—after the body has had time to excrete the excess fluids—when calculating weight change.

A more recent 2016 study of weight change in nearly 150,000 healthy babies found that it is “not uncommon” for newborns to be below their birth weight at 10 to 14 days after delivery. About half of newborns were at or above their birth weight at 9 days (vaginal delivery) or 10 days (cesarean section). However, about 14 percent of babies born vaginally and 24 percent of those born by cesarean had not regained their birth weight by day 14.

What the numbers on the scale don’t reveal is whether newborn weight loss is physiologic (a normal occurrence) or an unintended outcome—the consequence of a myriad of policies, procedures, and practices that not only fail to support, but often undermine, breastfeeding..

Does weight really matter? 

Weight is a measure of nutrition. When babies get too little food, too much food, or the wrong type of food they can become malnourished. Our understanding of how malnutrition affects brain development has changed considerably since the mid-1960s when it was thought that underfeeding could cause irreversible brain damage. Today, experts agree that a brief period of underfeeding (days versus weeks or months) is unlikely to cause permanent damage. 

It can, however, have serious short-term consequences. Timing seems to be the key factor, since even a brief period of underfeeding in the first days after birth can lead to hyperbilirubinemia (jaundice) and hypoglycemia (low blood sugar). 

Parents’ concern over weight is easy to understand, given that it is the only reliable indicator of growth. However, the number of wet and poopy diapers and breastfeedings can also be revealing and are much easier to measure.

As long as you are aware of the other signs that your baby is getting enough to eat, it’s easy to forgo the expensive in-home baby scale. A well-fed baby will: 

  • be active and alert 
  • be satisfied after breastfeeding 
  • breastfeed at least 8–12 times during each 24-hour period 
  • have 3 or more poops a day, by day 3 
  • have yellow poop by day 5 
  • have clear or pale yellow pee, and 6 or more wet diapers a day, by day 5

As long as you see these indicators of good health, there’s generally no reason to worry about having your baby’s weight measured in-between well-child visits.

What if my baby suddenly stops gaining weight? 

As long as your baby is reaching her developmental targets and isn’t losing weight, there’s no need to worry about a pause in weight gain. Weight loss, however, can be a sign that your baby isn’t getting enough to eat or is sick. Children who fail to gain an adequate amount of weight in the first nine months will usually catch up over time. So parents seldom need to increase their child’s calories (by supplementing with donor milk or artificial infant formula) unless their child is showing signs of malnutrition such as developmental delays or unexplained weight loss. Consuming too many calories in infancy can actually lead to weight problems later in life. 

Check out our developmental milestones guide to see if your baby is on track and if you are concerned about her weight and/or growth patterns, make an appointment with her health care provider.

Last updated December 21, 2016

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