From the day they are born to the first birthday, babies double their birth size and gain three times their birth weight. Judging babies' rate of growth is a helpful way to determine whether they are thriving as they should be. Babies come in various shapes and sizes, however, so figuring out a "normal baby weight" isn't simple. Various factors influence babies' initial weight and the rate at which they grow in their first year.
Normal Newborn Weight
According to KidsHealth online, the average full-term baby---born between 37 weeks and 40 weeks---weighs between 6 pounds 2 ounces and 9 pounds 2 ounces. A newborn who weighs more or less than the average weight range may indeed be a "normal" weight, but he may need to be examined for any potential underlying issues.
The First Week
The average baby will lose between five and 10 percent of her birth weight within the first seven to 10 days after birth. This is mainly because she has been born with some extra fluid in her body. Breastfed babies tend to lose more weight in this period than bottle fed babies because their moms may not have a lot of breast milk in the beginning. A bottle fed baby shouldn't lose more than about five percent of her birth weight.
The First Year
A healthy baby is back to his initial weight after about two weeks. For the final two weeks of his first month, he will have likely gained weight at a rate of between four and seven ounces per week. Sometimes a baby will gain rapid weight between seven to ten days old and then at three and six weeks. By the time a baby is one month old, he will gain between 1.5 and 2 pounds every month. Between four and six months, he will likely have doubled his birth weight. Your baby will be at about triple his birth weight by the time he turns one.
Growth Charts
Pediatricians usually gauge normal baby weight and growth by using growth charts. After weighing and measuring a baby, a pediatrician will use one of these charts to decide where she falls on the chart in comparison with other babies of her age. If a baby is in the 20th percentile for weight, 20 percent of babies of her age weigh the same amount or less, and 80 percent weigh more than she does. Variations come into play, such as if a baby was born prematurely. In this case, the pediatrician will likely judge her length, weight and head circumference based on her gestational age. If she was born three weeks early, she would be compared with babies three weeks younger than her.
Other Factors Influencing Weight
Besides prematurity, other factors affect a baby's weight. The baby's gender, the baby's health, the mother's health, the mother's nutrition during pregnancy, genes, multiple births, and birth order (such as being a first born versus a second child for the mother) may affect the baby's weight and growth rate.
