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Understanding Baby Growth Percentiles

Grow, Baby, Grow!

It’s part of the normal routine of well-baby care: Your pediatrician measures your child’s length, weight, and head circumference and notes them on a chart. You eagerly await the results, excited to hear that your bundle of joy is in the 90th percentile for height (Wow!), the 80th percentile for weight (Cool!), and the 75th percentile for head size (Ooh!). But what do these numbers really mean? Why are they important? Can they predict what your child will be like in the future?

If you’re confused, you’re not alone. Here’s everything you need to know about baby growth percentiles: where they come from, what they reveal about your child’s health, and when you should be concerned.

Measuring Up

Pediatricians in the United States began using government charts to measure babies’ growth in 1977. The National Center for Health Statistics created the first set of charts to give doctors a simple tool they could use to monitor normal baby growth development, but the charts were based on a small study of formula-fed babies in one area of Ohio—and some of the statistics came from as early as 1929.

In 2000, the US Centers for Disease Control and Prevention (CDC) released new-and-improved baby growth percentile charts. These updated charts—currently used in most American pediatric offices—are based on a national survey of children from various regions and ethnic groups, and babies fed through breastfeeding as well as formula-fed babies are included.

P is for Pattern

When your doctor plots those dots on your baby’s growth chart, she gets an instant snapshot of how your infant compares to other American babies of the same age. Separate charts are used for each gender, so your daughter will be compared to other baby girls and your son to other baby boys.

The “percentile” simply reveals where your baby growth ranks in comparison to the national survey. For example, if your daughter is in the 25th percentile for weight, that means she weighs more than 25 percent of baby girls her age, and less than 75 percent of baby girls her age.

There’s no need to nibble your nails with worry about the percentile numbers you hear at any one office visit. “The important thing is the pattern over time,” says Bradley S. Miller, MD, PhD, assistant professor of pediatric endocrinology at the University of Minnesota. “Looking at one point in time is not as helpful as looking at the comparison from one time to another.”

According to the American Academy of Pediatrics, in a healthy, well-nourished baby, the height, weight, and head-size measurements will increase at a predictable rate, creating a curve along the growth chart. Each child is unique, so your pediatrician expects your baby to follow her own unique curve. How she compares to other babies isn’t nearly as important as, “Is she still following her own established pattern?”

Highs and Lows

Even if your baby falls at the extreme high or low end of the chart, there’s usually no cause for alarm. “A healthy child can fall anywhere on the chart—even above the 97th percentile or below the 3rd percentile. They’re just at the edges of the norm,” Dr. Miller says.

What’s important is that the height and weight percentiles should fall in roughly the same neighborhood. If your daughter is in the 10th percentile for weight and the 25th percentile for height, everything’s probably fine and she just happens to be petite. However, if she’s in the 10th percentile for weight and the 90th percentile for height, your doctor might become concerned and monitor her nutritional intake more closely.

Keep in mind that, while nutrition is important, genetics plays a huge role in how your baby grows. According to Dr. Miller, a child will usually mirror the growth pattern of the same-sex parent. That means if you were tall and thin at 18 months, your daughter probably will be, too. And if you’re concerned that your toddler son is on the short side, ask your mother-in-law to dig out your husband’s baby photos. Chances are, he looked the same at that age. Like mother, like daughter. Like father, like son.

Leaps and Bounds

It’s not unusual for an infant to change percentiles between office visits. A baby grows by leaps and bounds between his first newborn exam and his first birthday. My daughter tripled her birth weight in her first year, leaping from the 50th percentile to the 75th percentile to the 80th percentile by her 12-month checkup.

However, if there’s a sudden, extreme change, especially if your baby drops percentiles—for example falling from the 75th percentile to the 25th percentile—it may indicate a problem. “[Your child] should be following a curve, not deviating from a curve,” Dr. Miller says. When a child’s growth suddenly slows down, it may mean that illness, a nutritional problem, or a hormonal problem is affecting the ability to grow.

Keep in mind, though, that a lot depends on the accuracy of the measurements at each visit—and a kicking baby or wriggling toddler can make it difficult to get accurate measurements. And another point to remember: It’s normal for growth to slow down after age one. While it’s not unusual for babies to gain several pounds between office visits, your toddler might gain only four or five pounds total between 12 and 24 months.

Head Room

When it comes to the head-size measurement, your pediatrician is simply making sure that your child’s brain is growing at a healthy rate. A head that doesn’t grow fast enough can reflect poor brain growth, while a head that grows too quickly can indicate possible developmental problems.

Again, genetics play a role, so what’s “normal” for your baby depends on what’s normal for your family. In our family, we’ve always had trouble finding hats big enough to fit our “generous” heads—and sure enough, my 18-month-old daughter wears a size 4T hat. Between ages two and three, you can expect your pediatrician to stop measuring your child’s head circumference, because most of the brain’s physical growth is complete by that age.

Dreams of the Future

Should you count on a basketball scholarship if your baby boy is above the 95th percentile for height? Not so fast. It’s a little early to start planning his career in the NBA. According to Dr. Miller, growth patterns in the infant and toddler years aren’t always an accurate predictor of how your child will look as an adult. A baby who’s at the top of the charts in infancy might experience slower growth later in childhood, while a baby who’s at the lower end of the charts might enjoy a major teenage growth spurt.

Percentiles are just one of many tools your pediatrician uses to monitor your child’s health. As long as your little one is making consistent forward progress and following his own unique pattern, chances are excellent that he’s growing just fine.

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