When Should a Baby Double Their Birth Weight?

Typical Growth Patterns and Other Ways to Tell if Your Baby's Weight Gain is Healthy

During their first year of life, babies grow and develop at an astounding rate, eating around the clock, outgrowing clothes from one week to the next and transforming from tiny, delicate newborns to robust almost-toddlers full of personality in the blink of an eye. In fact, most infants double their birth weight within their first 5 months of life, and many do so by the time they are only 3 or 4 months old.

In the exhausting early days of parenthood, it's very common to be concerned about whether your baby is growing, gaining weight and meeting other milestones at the expected rate. Of course, every baby is different, but when it comes to weight gain, a medical professional will routinely compare your infant's growth rate against predictable patterns. Gaining weight at a faster or slower rate than average doesn't usually indicate a problem, but your pediatrician will certainly consider any unusual patterns while assessing your baby's overall picture of health. Regular checkups and weigh-ins during the first year of life are the best way to be sure that your new baby is thriving.

Typical Infant Growth Milestones

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Normal Weight of Four- and Five-Month-Old Infants

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Most babies born full term weigh 6 to 9 pounds, and within the first three to four days lose some weight. During a newborn's first few days of life, a weight loss of around 5 percent is considered normal for a formula-fed baby, and 7 to 10 percent for a breastfed baby. Babies born full term are expected to return to their birth weight within 10 days to 2 weeks. For preemies or babies who have been sick, it's normal to take up to 3 weeks to get back to their birth weight.

According to the World Health Organization, from birth to 5 months, an infant is expected to gain 5.5 to 8.5 ounces per week. From 4 to 6 months, the average weight gain is 3.25 to 4.5 ounces per week, and from 6 to 12 months, it ranges from 1.75 to 2.75 ounces per week.

Your pediatrician expects your baby to double his birth weight by 5 months and triple it by 12 months. However, many babies double their birth weight within 3 to 4 months.

Reasons for Faster or Slower Weight Gain

If an infant loses more weight than is considered healthy during her early days, or doesn't reach her birth weight as soon as expected, it indicates a possible feeding issue that must be addressed. For newborns, such issues include a poor latch while breastfeeding, a nursing mother's low milk supply or a need to increase the frequency of bottle feedings. For babies of any age who don't meet their growth milestones, it's important to consult with a medical professional for the best course of action.

Be aware that expected rates of infant growth are based upon averages, but it's perfectly normal for weight gain to fluctuate. Babies grow in spurts and might gain no weight for a week or more or even lose weight, then gain a lot more than average the following month, all while still being perfectly healthy. Well baby exams are scheduled to provide an overall picture rather than a snapshot of a limited time period.

Differences Between Breastfed and Formula-Fed Babies

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The Size of a Newborn Baby

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Scientific studies show some significant differences in growth patterns between breastfed and bottle-fed infants. These differences begin to show statistically around 4 months of age. Overall, breastfed babies are leaner and gain weight at a slower rate compared to formula-fed babies from 4 to 6 months of age. Formula-fed infants double their birth weight slightly earlier on average than breastfed babies. After this time, they tend to weigh more on average as well.

Judging Your Infant's Health at Home

If you chose to, or are advised to, weigh your baby at home to assess her weight gain, be sure to use the same scale and dress your baby in the same amount of clothing every time you weigh her. Know that other factors affecting your baby's weight (other than diet) include hereditary factors such as body type and metabolic rate, along with temperament and movement. An energetic baby who moves around a lot, for example, will burn calories faster and might gain weight more slowly than a sedentary baby.

In addition to a healthy rate of weight gain, other indicators of healthy growth include:

  • Being eager to nurse or drink a bottle
  • Regular wet and dirty diapers
  • Bright and alert eyes while awake
  • Healthy-looking skin color and texture
  • Plenty of movement
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