All babies grow at different rates, though they seem to grow overnight during the first few months. After the initial growth spurt, growth slows down considerably. As long as a baby is following his own growth curve and meeting developmental milestones, then growth is most likely normal. A variety of factors influence the rate of a baby's growth.
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Breastfed babies gain weight quickly during the first few weeks, but then slow down considerably and are leaner overall compared to formula-fed babies. During the first month, a breastfed baby grows approximately four to seven oz., 112 to 200 g, per week, or approximately one-half to one oz. per day. From months two to six, babies gain an average of one to two lbs. per month, and from six months to one year, the average weight gain is one lb. per month. From the time they are born until their first birthday, babies grow by approximately nine inches -- one inch per month for the first six months and a half inch for each month after.
Formula-fed babies follow a different growth curve than their breastfed counterparts. This is because formula has a different composition than breast milk. This in turn can affect a baby's fat composition. During the first few weeks, formula-fed and breastfed babies growth is similar. After six months, a formula-fed babies gain weight more quickly and are, on average, one lb. heavier than breastfed babies by one year.
Babies don't grow at a constant rate. Sometimes it seems as though a baby is the same size for several weeks, and a day later, clothing no longer fits. This is because babies go through growth spurts. Certain times are common for babies to have growth spurts -- seven to 10 days old, around three weeks, six weeks, three months, four months, six months and nine months. Some babies go through growth spurts at each of these times, others skip some or have a growth spurt at a different time. A typical growth spurt lasts two to three days.
The Role of Genes
A baby's genetic make-up plays a large role in her body type and growth rate. For the most part, there is nothing you can do if you have a plump or lean baby. Generally, a baby follows the characteristics of his parents. If both parents are petite, then it is likely that the baby will also be petite. If both parents are very tall and broad, then their baby will probably grow at a fairly fast rate and also be tall.
Sometimes babies don't grow at a proper rate. This is called failure to thrive and is observed when a baby is below a normal weight, most often when a baby is below the third to fifth percentile, or she weighs less at a particular age than 95 to 97 percent of babies the same age and gender. Failure to thrive can be caused by levels of growth hormone that are too low, or by other diseases or conditions. Only a doctor or pediatrician can diagnose and treat this condition.