ACOG gestational dating guidelines
ACOG Committee Opinion No. 700 designates gestational age as the primary metric for clinical obstetrics in the United States. Gestational age begins at the first day of the last menstrual period, representing 280 days of gestation.
ACOG categorizes term deliveries into early term (37 0/7 weeks to 38 6/7 weeks), full term (39 0/7 weeks to 40 6/7 weeks), late term (41 0/7 weeks to 41 6/7 weeks), and postterm (42 0/7 weeks and beyond).
Standard US prenatal visits occur every 4 weeks through week 28, every 2 weeks through week 36, and weekly until delivery, with universal gestational diabetes screening performed between 24 and 28 weeks.
Worked example: US prenatal timeline
For a patient with an LMP of October 1st and regular 28-day cycles, the EDD is July 8th.
The first trimester ends at 13 weeks + 6 days, anatomy ultrasound is scheduled at 18–20 weeks, and full-term status is reached on June 24th at 39 weeks.
US pregnancy inputs
Dating Reference
Select LMP, conception, or ultrasound scan measurement.
CALCULATOR QUESTIONS
ACOG pregnancy due date & trimester calculator questions
Why does ACOG define full term as 39 weeks instead of 37 weeks?
Research demonstrates that infants born between 39 weeks 0 days and 40 weeks 6 days have lower rates of respiratory morbidity, NICU admissions, and neurodevelopmental complications than infants born at 37 or 38 weeks.
When should I notify my employer about FMLA leave?
Under the Family and Medical Leave Act (FMLA), you must provide your employer with at least 30 days advance notice when your leave is foreseeable.