Infant weight gain is one of the most important indicators of an adequate milk supply. However, it's normal for babies to lose 5 to 8 percent of their birth weight during the first few days of life. After that, babies gain about one ounce of weight per day, and by their two-week checkup, they should surpass their birth weight by a few ounces. A baby who weighs less than his birth weight at his two-week checkup might not be feeding adequately.
Breastfed babies gain weight more rapidly than formula-fed infants during the first two months of life, then slow down around the fourth month. By six months of age, their birth weight should have doubled. If you have concerns about your baby's weight, call your doctor. You can have your baby weighed any time.
Too often, parents are concerned when their infant is in the low or high end of the growth chart for their age. Growth charts were developed using formula-fed infants as the baseline, so don't worry if your baby weighs in lower than “normal” on the chart.