About one third of PTBs occur because early delivery is indicated due to complications in the mother or the unborn baby (fetus); the remaining two thirds occur spontaneously. The rate of PTB has increased by 19% from 1990 to 2010 in developed countries. At the same time, there has been a marked improvement in the survival rates of PTBs but a similar reduction in adverse outcomes has not been seen. Thus, the absolute numbers of individuals adversely affected is increasing.