preterm birth classification
This website looks quite interesting:
http://www.marchofdimes.com/professionals/14332_1157.asp
http://www.marchofdimes.com/professionals/14332_1157.asp
Most premature babies (71.2 percent) are born between 34 and 36 weeks of gestation (1). These are called late preterm births. Almost 13 percent of premature babies are born between 32 and 33 weeks of gestation, about 10 percent between 28 and 31 weeks, and about 6 percent at less than 28 weeks of gestation (1).