When you and your baby go in for your first wellness check-up after birth, don’t be alarmed if she has lost a little bit of weight. It is completely normal for formula-fed newborns to lose up to 5% of their body weight, and breastfed newborns to lose between 7% and 10% of their body weight in the first 5 to 7 days of life. Most newborns will return to birth weight by their tenth to fourteenth day of life.
In breastfed newborns, a large part of this weight loss is caused as your baby adjusts to the shift in milk content. Colostrum is the first breast milk your body produces, and it has a yellowish color, as well as a higher fat content and more concentrated nutrients than transitional and mature breast milk. Colostrum changes to transitional milk over the first 2 to 5 days, then mature milk by the end of the first couple of weeks. Another reason why both breastfed and formula-fed newborns can tend to lose weight is that they are not born with the skills they need in order to eat, after having spent all their time in the womb receiving what was essentially IV nutrition. Sometimes it takes them a little while to get the hang of it, either by not feeding as efficiently as they could, or by falling asleep mid-feed or sleeping through feedings, which can trick new parents into thinking they're full when really they could use a bit more to eat. Some newborns lose additional birthweight by shedding the water weight gained through IV fluids mom received during labor.
Your newborn losing weight may seem like a big problem, when in actuality it’s quite common - almost the norm, even. However, if your baby is losing weight, seems overly sleepy all the time, and isn’t producing about six wet diapers, and three or four dirty ones throughout the day, this may be cause for concern. If you are concerned about her weight loss, you can always ask the doctor, as he or she will have a vast amount of experience dealing with baby weight.