Post maturity is defined as a pregnancy which has continued for 42 weeks or longer after the date of the last menstrual period. Such pregnancies may be more at risk of developing complications as a result of decreased placental function trying to support a bigger baby, and difficulties with delivery. The timing of delivery is determined by a combination of factors, some of which derive from the mother and some from the baby. Why some infants appear reluctant to leave the warmth of the womb and enter the world is uncertain.