Preterm or premature labor is when there are contractions and cervical changes before 37 weeks gestation. Preterm labor is diagnosed when contractions begin and intensify between the 20th and 37th week of gestation. Preterm labor can lead to the birth of a premature baby or the birth of a baby that is not viable if born before the 27th week of gestation. In most cases of preterm labor, the contractions begin spontaneously and without definitive cause. Preterm labor offers a unique set of challenges for both mom and baby.