Pounds and inches obsess parents of babies. Here, pediatricians give the facts on growth during the first year and answer the most common questions parents have about baby growth percentages.

By Sarah McCraw Crow and Hallie Levine Sklar
Monkey Business Images/Shutterstock

As parents, we watch our babies grow with awe. Yet few of us can resist comparing our child with others his age. We wonder: Is my chubby son destined to be fat? Is that taller, heavier baby healthier than my smaller, lighter child? Is the fact that my daughter isn't crawling a sign that she's developmentally behind?

The answers are no, no, and no. Furthermore, all of those comparisons won't tell you much about your own baby's progress, says Ben Danielson, M.D., medical director of Odessa Brown Children's Clinic, in Seattle. Like grown-ups, babies come in a multitude of "normal" shapes and sizes. And they hit developmental milestones according to their own inner timetables.

So bottom line? Don't stress about your child's specific percentile. Here, pediatricians share the nitty-gritty on growth — and put your worries to rest — by answering the most common questions about baby growth percentages.

What does my baby's percentile mean?

At each checkup, your baby's weight, length, and head circumference are plotted on a growth chart. If your child’s height is at the 75th percentile, for instance, it means that he is as tall as or taller than 75 percent of the boys in his age group.

Any number between the fifth percentile and the 95th is considered normal. Whether the measurements are high or low, they should follow a consistent curve over the first year.

"Your baby's position on the chart means very little to us," says Robert Eden, M.D., a clinical assistant professor of pediatrics at Brown University Medical School, in Providence. "What matters is whether she's growing in a predictable trend." There are bound to be variations from checkup to checkup, but any dramatic change (a drop from the 50th percentile to the fifth, for instance) is a red flag, and your doctor will want to keep closer tabs on your child.

What if my baby is below the 50th percentile?

If your baby is below the 50th percentile in weight, you may be tempted to try to feed her more. Don't, advises Dr. Eden. Even babies below the "normal" range will be fine as long as their growth remains steady.

"My 10-month-old's measurements have been in the third or fourth percentile since her birth," says Chris Anne Wheeler, a mother of two from Hopkinton, New Hampshire. "She has her own growth curve that parallels the usual curve."

In addition, babies of Asian, Hispanic, and Pacific Islander backgrounds tend to be smaller, on average, than babies of other ethnicities. While the newest growth charts incorporate data from diverse racial and ethnic groups, you should still take your child's background into account.

What if my baby is above the 50th percentile?

We've all read the statistics about the boom in childhood obesity. But don't panic about your 6-month-old's chubby thighs. Your baby's weight does not predict future obesity unless it is radically out of proportion to his height. And no matter what your baby weighs, never restrict his food intake; he needs calories and fat so his body and brain can grow.

"Having a large baby is often just a sign that everything went well during your pregnancy," says Daniel Rauch, M.D., associate professor of pediatrics at Mount Sinai School of Medicine, in New York City. (Your baby may have also been uncharacteristically big if you suffered from gestational diabetes.) But once he's out of the womb, genetics take over, and unless he's got supersize parents, he'll show his true growth patterns between 9 and 18 months.

Should my baby's height and weight be in the same percentile?

Conventional wisdom holds that a baby's height, weight, and head circumference should be in the same percentile. While that's often the case, don't fret if your baby's percentiles seem out of whack.

"Both scenarios are common," says Cynthia Ferrell, M.D., an assistant professor of pediatrics at Oregon Health & Science University, in Portland. During a growth spurt, a baby's length may shoot up, or he may gain weight quickly, causing his growth-chart percentiles to diverge.

Should I be concerned about a big head?

Of all your child's organs, her brain grows most rapidly, with the head expanding right along with it. That's why your pediatrician so conscientiously measures head circumference — to ensure that the brain is developing properly. One way to tell that a baby is significantly undernourished is that she stops gaining height and weight, while her head continues to grow at a normal rate (the body automatically reserves calories for all-important brain growth).

If a baby's head seems particularly large in relation to her height and weight, the doctor may measure the parents' heads, since this characteristic runs in families.

Will my preemie catch up to an average percentile?

Although babies born preterm (before the 37th week of pregnancy) are small at birth, they grow faster than full-term newborns — most likely because they're completing what would have been their in-utero growth. By 2, most premature babies have caught up with their full-term counterparts.

But there are exceptions. Being a multiple or being extremely premature, for example, can affect a baby's future size, says John Walburn, M.D., a professor of pediatrics at the University of Nebraska Medical Center, in Omaha. "Some of the smallest preemies never quite catch up, no matter how well nourished they are."

What if my child isn't growing?

"Failure to thrive" is a scary phrase that pediatricians use when a baby, toddler, or preschooler loses weight.

"We're not worried about the short-term effects of a stomach bug, but if your child drops significantly on the weight charts, your doctor should notice," says Lynnette Mazur, M.D., professor of pediatrics at the University of Texas in Houston.

Your doc will discuss strategies to improve his diet. Failure to thrive can also indicate an infection, hormonal issues, an allergy, or a chronic disease such as diabetes, so if your child is dropping weight, consult your pediatrician.

If my child doesn’t sleep well, will it stunt his growth?

Kids need rest to thrive; their body releases growth hormone during sleep. But even if your child refuses to nap or wakes often at night, he's likely getting enough sleep to grow. If your child is a snorer or a mouth breather or pauses in his breathing when asleep, tell your doctor. These are signs of sleep disordered breathing, a treatable condition affecting about 20 percent of kids.

How much does diet impact growth?

"Genes are the most important factor, but you can't reach your genetic potential if you're not adequately nourished," explains Dr. Rauch.

If she is eating a balanced diet, your child probably doesn't need a multivitamin. However, the American Academy of Pediatrics recommends that all infants, children, and adolescents get a daily dose of 400 IU of vitamin D, which is essential for healthy growth. Since it's hard to get enough vitamin D from food alone, your child will probably need to take a daily supplement soon after she is born, unless she gets at least 34 ounces of D-fortified formula per day.

Should I be worried if my baby suddenly gains or loses weight or height on a growth chart?

Probably not. Though growth charts help in spotting such fluctuations, the reality is that a baby's growth is often marked by variation -- some will have a nice even curve, and some will have peaks and valleys. Because they grow in leaps, it's normal for babies to slide up and down the charts a bit as part of typical 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. 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.

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