Premature birth is defined as birth before the 36th completed week of pregnancy. The earlier the birth the greater the risks to the infant. Babies born after 32 completed weeks usually do very well indeed after birth, and the risks of complications rises progressively for babies born below 32 weeks, although advanced neonatal care has dramatically improved the outcome. Babies born between 26 and 28 weeks are now estimated to have an 80% chance of survival, with 70% of survivors having no disability.
An important difference between being born too small (SGA) and being born too soon (prematurity) is that premature babies may have all the problems of an SGA baby, but have additional problems due to the immaturity of all the major body systems – bowels, kidneys, circulation, lungs, immunity and brain.