Being born early means a baby has less time in the mother s uterus to grow and gain weight. Much of a baby s weight is gained during the latter part of pregnancy. This occurs when a baby does not grow well during pregnancy because of problems with the placenta, the mother s health, or birth defects. Babies with IUGR born at term may be physically mature but may be weak. Premature babies can also have IUGR these babies are both very small and physically immature.
Any baby born prematurely is more likely to be very small.
However, there are other factors that can also contribute to the risk of very low birthweight. Over half of twins and other multiples have low birthweight. Mothers of lower socioeconomic status are also more likely to have poorer pregnancy nutrition, inadequate prenatal care, and pregnancy complications - all factors that can contribute to low birthweight. A baby with low birthweight may be at increased risk for complications. Because they have so little body fat, low birthweight babies often have difficulty staying warm in normal temperatures.