How Does Your Baby Grow?

Is your infant small for his age -- or topping the growth charts? Here's what all those measurements mean.

Answers to Your Most Common Questions

Q: How were the growth charts compiled, and how should parents use them?

A: The charts (one for boys, one for girls) were devised by the federal Centers for Disease Control, in Atlanta, on the basis of 31 years of data collected from thousands of children. The recently updated tables (see The New Growth Charts) track the growth of healthy kids from birth to 20 years of age by plotting height, weight, and head circumference.

The purpose of the charts isn't to compare your child with others -- generally, any weight or height between the 5th and 95th percentiles is considered normal. Instead, physicians use the stats as a reference point -- watching for consistent growth over time. "A baby can remain in the 5th percentile for any of these measurements indefinitely and still be considered healthy, as long as he continues to grow," says Mark Widome, M.D., a professor of pediatrics at Pennsylvania State University, in Hershey, and a Parents advisory-board member.

Q: My husband and I are short, but our baby is in the 90th percentile for length. Will she be tall?

A: "A child's length at birth does not necessarily indicate future height," says Frank Greer, M.D., a professor of pediatrics and nutritional sciences at the University of Wisconsin at Madison. "Small parents can have a very large baby, for reasons related more to intrauterine nutrition than to genes. For instance, a short mother with even a mild case of gestational diabetes can have an infant who is large for his age, not only in terms of weight but in length and head circumference as well." Still, family traits come into play fast: "In the course of the first year, usually by the second half, a baby's growth will probably fall more in line with his parents' patterns," Dr. Widome says.

Q: My baby is in the 10th percentile for weight. Should I supplement her feedings to try to get her closer to the 50th percentile?

A: "Growth charts do not represent any ideal, and bigger is not necessarily better," says Lawrence Hammer, M.D., an assistant professor of pediatrics at Stanford University School of Medicine, in Stanford, California. Small babies should be fed the same as larger ones and watched only for steady weight gain. Similarly, a large baby who is growing consistently should not be put on a restricted diet.

Q: Is a rapid gain in height or weight any cause for alarm? How about an unexpected drop-off?

A: Though growth charts help in spotting such fluctuations, the reality is that an infant's growth is often marked by variation. "We look for patterns -- some babies follow a nice even curve, and some have a pattern of plateaus," says Barbara Fritz, a dietitian in Greenfield, Massachusetts, who works for the Women, Infants, and Children program (serving at-risk mothers and children) in the western part of her state.

Because they grow in leaps, Dr. Widome says, "infants can move up and down the charts a bit as part of normal growth patterns." The key is how fast and drastic the transition is. "If your baby has been at the 50th percentile and drops to the 5th, for instance, the doctor will want to explore why the growth pattern has been interrupted," he says. Possible causes include illnesses such as diabetes or other endocrinologic problems. There are also conditions that could lead to a dramatic jump in growth. More often, though, the cause is a growth spurt or improved nutrition.

Q: Should my infant's height and weight fall in the same percentile?

A: These two measurements should correspond closely -- you'd expect a baby in the 60th percentile for height to be near the 60th for weight as well. The new growth charts have an index that gauges whether an infant's weight correlates desirably with his height.

Q: Why is my baby's head measured at every visit? What if her head is in the 90th percentile while her height is in the 50th?

A: A baby's brain and head do 80 percent of their growing during the first two years. Measuring head circumference helps doctors track the brain's growth as the skull bones knit.

Rest assured, it's not uncommon for a baby's head size to seem disproportionate to her height and weight. The usual explanation is genetics: If a baby's parents have big heads, the baby will probably have one too. The head's size relative to the rest of the body is less important than a consistent pattern of growth.

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