Babies grow astonishingly fast. By your little one's first birthday, he'll have tripled his birth weight and grown eight to ten inches. Even his head—which is about one third the size of an adult's at birth—will grow faster in his first four months than at any other time. "A child grows more rapidly during his first 12 months than in any other period of his life," says Gregory Plemmons, M.D., medical director of the pediatric primary-care practice at Vanderbilt Children's Hospital, in Nashville. "What's interesting is that these increases in weight and height aren't slow and steady—they appear to happen in fits and starts."
Researchers are still trying to figure out exactly when and how these periods of growth occur. Some experts think that they last between two to seven days and happen at predictable ages—10 days, 3 weeks, 6 weeks, 3 months, and 6 months. Others say there's no set schedule and that the timing varies from baby to baby. But moms recognize a growth spurt when they see one. "I've had mothers swear that their babies grew overnight," says Michelle Lampl, M.D., Ph.D., a growth researcher and associate professor of anthropology at Emory University, in Atlanta. "They tell me their child's legs were suddenly longer or the diaper or socks seemed much tighter." Dr. Lampl's own research backs them up: She's found that babies can gain a whopping one to three ounces and grow almost a centimeter in length in 24 hours, followed by days to weeks of almost no growth at all.
So how can you tell when your baby is going through a growth spurt? Here's what to look for:
Sharon Kelley knows when her 4-month-old daughter is having a growth spurt. "Suddenly, she wants to nurse nonstop," says the mom from Westford, Massachusetts. "Instead of sleeping through the night, she wakes up every two to three hours to eat. During the day, she'll want to feed every hour or two." Experts agree that a sudden jump in appetite is the most telling sign of a growth spurt. "Out of the blue, a baby who was nursing at regular intervals wants to spend the entire day at your breast," says Katy Lebbing, a lactation consultant with La Leche League International. Formula-fed infants may appear dissatisfied after finishing a bottle and want to eat several more times during the day and night.
These feeding frenzies serve two purposes: "A growing baby is a hungry baby—she needs all the calories she can get," Dr. Lampl says. Second, if you're nursing, frequent feedings boost your milk supply so you can meet the increasing appetite of a larger baby. Don't be surprised if your little one wants to nurse as often as 15 or 16 times a day during a spurt. "Short, frequent breastfeeding sessions build a mother's milk supply much more effectively than longer, infrequent ones," Lebbing says.
My 10-month-old got very irritable whenever he went through a growth spurt," says Denise Swanson, of Maquoketa, Iowa. "He became cranky and restless, and nothing I did seemed to soothe him." The most obvious reason for this moodiness? Lack of sleep. "If he's awake more often during the night in order to feed, he's not getting the longer periods of rest he needs—which will put even the calmest baby on edge," Dr. Plemmons explains.
After several days of nonstop eating, your baby may sleep more soundly than usual. "That's when we think growth occurs," Dr. Lampl says. Research shows that nearly 80 percent of growth hormone is secreted during slumber. "Your baby needs sleep to enable her body to produce those hormones," says Joan DiMartino-Nardi, M.D., a pediatric endocrinologist at the Children's Hospital at Montefiore Medical Center, in the Bronx. Never force a baby to stay awake or adhere to her normal sleep schedule—you'll only make her cranky. Plus, she needs all the energy she can muster to keep growing.
Don't be too quick to blame growth spurts for everything. Have you recently changed his caregiver or his daily routine? Your child may be seeking comfort the same way adults do—by snacking and snoozing more. He could also be getting sick: Breast milk provides valuable antibodies that your baby needs to fend off an infection, while sleep gives the body energy for the fight. In addition, a baby who is teething may become fussier and display erratic changes in his eating and sleeping patterns. Finally, don't forget the simplest reason of all for sudden shifts in your baby's mood and schedule. "He's a baby—it's his job to constantly throw you for a loop!" Dr. Plemmons says. "Just trust your instincts and follow your baby's lead."