A maternal condition defined by the progressive dilation and effacement of the cervix that begins after 20 weeks and before term (the 37th week of pregnancy). This condition occurs because risk factors that are known or unknown cause uterine contractions and the cervix to dilate and efface prior to the time that the fetus is considered Term or 37-41 weeks. Many known and unknown causes for the condition exist. This condition is the leading cause of morbidity and mortality of newborns.