How Does Your Baby Grow? Answers to new parents’ top questions about birth weight, growth spurts, measuring up, and more By Laura Flynn McCarthy I’ll never forget the thrill I felt at my firstborn’s two-week checkup. "He’s gained one pound, six ounces," I announced to everyone within earshot. I figured I must be doing something right. Nine years and a second child later, I still feel the same excitement and anticipation at each of my children’s checkups, but I’ve learned that how much they grow has a lot more to do with their genetic makeup than with my mothering skills. One of my sons has been steadily in the 65th percentile of height and weight, and the other has hovered around the 10th, even though they eat generally the same foods each day. The doctor assures me that both are developing normally, just differently. Children’s growth patterns, while predictable in some ways, are as individual — and sometimes as quirky — as their personalities. To help you navigate the sometimes confusing path of childhood growth, here’s how pediatricians answer parents’ most pressing concerns. 1. Why did my baby lose almost a pound between his birth and when we took him home from the hospital? It’s common for a newborn to lose about 10 percent of his birth weight within his first two days, says Judith Groner, M.D., clinical associate professor of pediatrics at Ohio State University School of Medicine, in Columbus. It’s simply fluid that he no longer needs once he’s born. The amount of extra fluid varies by baby, so that some infants lose slightly more than 10 percent of their birth weight and others don’t lose any weight at all. Most regain what they shed within a week or two. Babies who are breastfed may take a few days longer to return to their original weight. That’s because it can be three or four days before a mother’s milk comes in, and several days after that for the baby to establish a regular eating pattern. 2. My 10-month-old seemed to gain weight like crazy during her first six months, but then she slowed down. Is this normal? Perfectly normal. Infants typically double their birthweight in their first six months, and then the growth rate slows by about half, so that at the end of the first year a baby’s weight has tripled. "Then, after the first year, the rate of weight gain drops dramatically," says Dr. Groner. 3. Is it true that breastfed babies gain weight faster than bottle-fed infants? Yes and no. Research shows that breastfed babies typically gain weight more rapidly than those formula-fed during the first two months (with the exception of the first few days). But from age 2 months to at least 6 months, that rate tapers off and the growth rate of formula-fed babies begins to surpass that of breastfed ones by 5 to 10 percent. By the time they turn 1, however, both bottle-fed and breastfed babies start to grow at about the same pace, says Nancy Butte, Ph.D., associate professor of pediatrics at Baylor College of Medicine, in Houston. "We don’t know why breastfed babies grow faster in the beginning," says Butte, "but some studies show that during that time they expend a bit less energy than formula-fed babies, so it could be that they’re just not burning off as many calories. Then, between 2 and 6 months of age, they don’t eat quite as much as before, so growth slows. By the end of the first year — when most moms have stopped nursing — babies are switched to cow’s milk and solid foods, so that both groups of children have similar diets. Whatever the reason for the different growth rates, both are well within normal, and parents needn’t be concerned." 4. All through his first year, my baby’s weight and height were in the 50th percentile. Now he’s 18 months old, and at his last two checkups he was much lower — in the 25th percentile. Could something be wrong? Probably not, especially if you or your partner aren’t especially tall or heavy. The rate at which a baby grows during his first year of life reflects the good prenatal care you’ve given him; his growth rate from then on mainly reflects his genetic makeup. If he stays around the 25th percentile, he’s most likely perfectly normal, says Dr. Groner. "If he keeps dropping into a lower percentile, however, there may be either a medical or nutritional reason why this is happening, and tests may be required to find out what’s causing the decline," she says. "But a child who grows consistently at the 10th percentile is just as normal as one who grows consistently at the 50th percentile, or the 75th." 5. How come the pediatrician measures the growth of my baby’s head? She’s making sure that it’s growing normally — not too fast (which can indicate hydrocephalus, a rare condition in which there’s too much fluid on the brain), too slowly (a sign of poor brain development), or in a lopsided fashion (which may mean the bones of the skull aren’t forming correctly). In most cases, the rate of growth of a baby’s head parallels his body’s growth rate, so if his weight and height are in the 50th percentile, his head circumference probably will be too. 6. Why does my baby’s head seem so out of proportion to her body? "During her first year, much of a baby’s weight is concentrated in her head," says Dr. Groner. "By the end of the first year, a child’s body usually catches up to her head, and she looks much more balanced." 7. My 6-month-old usually fits into size 12-month clothes. Is he going to be a big boy? Maybe, but better gauges of a child’s eventual height are his parents’ statures and which percentiles in height and weight he follows as he grows. Kids’ clothing sizes also vary widely by manufacturer, and same- size garments may fit differently depending on how your child is proportioned, so it’s difficult to use clothes to predict future size. 8. My 5-month-old has always been in the 50th percentile of weight and the 60th percentile of height, but at her most recent checkup, she jumped to the 75th percentile of weight and the 85th of height. What gives? She’s probably just experiencing a growth spurt. Babies typically gain about an ounce a day during their first six months, but this can go up at different times during growth spurts. If her weight and height stay in the higher percentiles, it could mean that eventually she’ll be fairly tall. 9. Is it true that if you double a 2-year-old’s height, you’ll find out how tall he’ll be later? That’s a common belief, but it’s never been proved. Since growth patterns typically are set by age 2, if a child has been in the 75th percentile for most of his second year, he’ll probably stay there until puberty. At that point, though, a child who’s always been in, say, the 5th percentile may shoot up and stay around the 25th percentile in adolescence and young adulthood, says William Cochran, M.D., associate professor of pediatrics at the Penn State Geisinger Health System. By the same token, being in the 75th percentile during childhood doesn’t necessarily mean a child will stay at a high level throughout the teen and young-adult years. In the end, a person’s ultimate height still depends a lot on how tall his parents and grandparents are. But second in importance to genetics is the age at which a child enters puberty, a period of very rapid growth over several years. Once it’s over, growth decelerates and eventually stops. So the more years of slow, steady growth before puberty, the taller a child will be. Late bloomers often end up taller than kids who enter puberty at an early age. 10. My 13-month-old was born six weeks premature, and although she’s healthy, she seems a little small for her age. Will she ever catch up to the other kids? Probably, but it may take a few years. Since she was a preemie, you should base her weight and height on the age she’d be if she’d been born on her due date. For example, if she was due on July 15 but was born on June 1, base her growth on what’s normal for babies born on July 15. "The earlier a child was born, the more that prematurity affects her growth," says Dr. Groner. "A child born 12 weeks premature has a lot more catching up to do than one born a month ahead of schedule." If your child is otherwise healthy, prematurity shouldn’t ultimately hinder her growth. Studies show that by age 8, preemies typically completely catch up in height and weight to children born full-term. An exception: Those born earlier than 32 weeks sometimes remain slightly smaller. 11.Is it normal for same-sex fraternal twins to grow at different rates? Absolutely. "Fraternal twins are no different in terms of growth than two siblings born at different times — in both cases, their genetic makeups are different," says Dr. Cochran. "Identical twins, however, usually grow at about the same rate and in similar patterns. In fact, if I suspect a growth problem in one child who’s an identical twin, the first question I ask is, ’How is his twin growing?’" At birth, fraternal twins are sometimes closer in weight and length than identical twins. "That’s because about one-third of identical twins share a single placenta in the uterus, and usually one baby is better nourished from it than the other," says Susan Griffith, M.D., staff family physician at the University of Kentucky, in Lexington. "It’s not unusual to see one identical twin weighing five pounds at birth and the other eight. But usually by the end of the first year, they’re both about the same length and weight, and will continue to be so throughout childhood and probably for the rest of their lives." When fraternal twins are different genders, the boys tend to weigh slightly more and be about one inch longer at birth than the girls; by 6 months, a girl twin weighs an average of one-and-a-half pounds less than her brother. 12. My 6-month-old refuses to eat the solid foods that I’ve introduced, such as rice cereal. Could this stunt her growth? Probably not. At this age, your baby is still getting most of her nutrition from breast milk or formula, and solids are more of a supplement. But you’re wise to at least introduce them by 6 months, as it can take weeks for some babies to warm up to the idea. If your child continues to turn her head away, ask her pediatrician about starting with a sweeter food, such as mashed bananas. Babies have a natural preference for sweet tastes, and starting off with one may be an easier entree into the world of solid foods than blander choices. Laura Flynn McCarthy, a New Hampshire-based writer who specializes in health and parenting issues, is the mother of two.