It is a good idea to maintain a growth chart for your baby. Most healthcare providers have charts with calculations indicating the healthy rate of growth. It is also a good idea to keep a watch at home, because a slow growth may be an indicator of poor nutrition or health.
Here are a few thumb rules to help you monitor whether your baby's growth is normal, which will indicate overall good health.
Baby growth percentile indicates the weight of your baby as compared to other babies. It informs you what percentage of babies weigh more or less than your baby. If your baby has a percentile weight of 40% it means that out of 100 babies weighed, yours weighs less that 60 other infants and more than 40 other weighed infants. If your baby's weight has a percentile of 50%, it means that this is the average weight of babies of that age. If it is less that 50% it means that your baby weighs less than the average weight; if your baby has a percentile is more than 50%, it means that your baby weighs more than the average. See also baby growth percentile
Percentile weight however, does not indicate whether your infant is over-weight or under-weight.
Babies who are born premature are smaller in length and weight, with a smaller head size. They also tend to lose more weight immediately after birth. But if they feed well and remain healthy, such babies tend to catch up with other babies by the end of two years.