Measuring the infant's height and weight is part of every well baby checkup, and parents are often concerned about their baby's growth. The height and weight of an infant is compared not only against other babies of the same age, but also against the child's own history. A baby who seems small or large for his age may be perfectly healthy if the weight and height gain is consistent from one doctor visit to the next.
Percentiles
When doctors measure the height and weight of an infant, they consider the results against an average of all babies of the same age to determine the percentile a particular baby falls within. A baby who falls into the 70th percentile for height, for example, is taller than 70 percent of her peers. The percentile for weight and height can be mismatched in some babies. For example, a long, thin baby may be above the 90th percentile in height but below the 10th percentile in weight. As long as the baby is gaining in both height and weight over time, this is considered a normal variation.
Rates
A baby typically loses weight during the first week of life, dropping up to 10 percent of his original weight, explains Kids Health. He will then gain approximately 2/3 of an ounce daily throughout the rest of his first month. This level of weight gain continues as he completes the first three months of life. After one month of age, most babies also gain an average of one to one and a half inches every month in height. According to MayoClinic.com, a baby should be double his birth weight at six months and triple it at one year.
Growth Spurts
Babies typically go through growth spurts at various times during infancy. According to What to Expect, a baby usually has at least five growth spurts during her first year of life. The first usually occurs between the first and third weeks of age. The second begins sometime around weeks six to eight. Babies of three months, six months and nine months also tend to have growth spurts. These growth spurts only last a few days, but frazzled parents may feel like the infant wants to eat constantly during this time, and may even notice the baby outgrowing clothes that fit fine a few days before.
Considerations
Sometimes the scale that the doctor uses to measure the baby affects his weight measurement, especially if different scales are used each time or if the scales are not properly calibrated. For premature infants, the weight and height are compared against babies of the same gestational age, since these infants start out smaller.
Related Concerns
In addition to height and weight, a pediatrician may look at other factors to determine the overall health of the infant. The amount of food a baby eats, how often she produces a wet or dirty diaper and the quality and consistency of her stool are other signs that can indicate how healthy she is at each checkup.
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