"Weeks matter," said Dr. Jeffrey Ecker of Massachusetts General Hospital, who chaired the ACOG committee that came up with the more specific labels. Since babies' outcomes can differ, "let's not call it all the same." The new definitions, released Tuesday in the journal Obstetrics & Gynecology: Early Term, between 37 weeks and 38 weeks 6 days. Full Term, between 39 weeks and 40 weeks 6 days. Late Term, the 41st week. Post Term, after 42 weeks.