The charts your pediatrician uses to monitor your baby’s growth are based on an average of formula-fed and breastfed babies of different ethnicities across the country. While those percentiles might sound intimidating, what they mean is actually simple: If your baby is in the 40th percentile for length, 40 percent of other American babies his age are the same length or shorter, and 60 percent are longer. Ditto for his weight.
Here’s the important point: Longer (or heavier) isn’t necessarily better, and shorter (or lighter) is not necessarily worse. “The charts are not a standard but simply a reference tool to gauge how the growth of a child or a group of children compares to that of the overall population of American children,” explains Cynthia Ogden, Ph.D., an epidemiologist for the U.S. Centers for Disease Control and Prevention.
When Not to Worry
Pediatricians are less concerned with percentiles than with seeing steady and consistent growth. For example, if your child is in the 10th percentile for his weight and he has always been at or around the 10th percentile, he is likely growing normally.
A sudden change in the percentiles is a red flag. “Concern is also prompted if a child is way outside the normal ranges, is not progressing normally or has disproportionate measurements,” says Phil Fischer, M.D., a pediatrician at the Mayo Clinic in Rochester, Minn. For example, a baby’s head circumference may be too small for his length. Even then, other factors, including changes in eating habits, growth spurts and illness, are considered.
How Your Baby Grows
Though all babies are different, here are some general guidelines:
- In his first six months, your baby may grow ½ to 1 inch a month and gain 5 ounces to 7 ounces per week.
- Your baby’s birth weight will probably double by 5 months to 6 months.
- From 6 months to 1 year, he may grow ⅜ inch a month and gain 3 ounces to 5 ounces a week.
- By age 1, his birth length may double and his birth weight may triple.
- Exclusively breastfed infants tend to gain weight faster in the first two to three months but weigh less than formula-fed babies from 6 months to 1 year.