What Is the Normal Gestational Age for a Healthy Full-Term Birth?

Full-term pregnancy is defined as gestation lasting between 39 weeks and 0 days and 40 weeks and 6 days—approximately 273 to 286 days from the first day of the woman’s last menstrual period (LMP). Deliveries occurring within this window are considered optimal for neonatal outcomes, with the lowest risks of respiratory morbidity, feeding difficulties, hypothermia, and neurodevelopmental complications.

Babies born at 37 weeks’ gestation or later are classified as “term,” but distinctions exist within that category: early term (37 weeks 0 days to 38 weeks 6 days), full term (39 weeks 0 days to 40 weeks 6 days), late term (41 weeks 0 days to 41 weeks 6 days), and postterm (42 weeks 0 days and beyond). While early-term infants generally fare well, evidence consistently shows improved organ maturation—particularly in the lungs, brain, and liver—between 37 and 39 weeks. Consequently, elective deliveries before 39 weeks are discouraged unless medically indicated.

Spontaneous labor most commonly begins between 39 and 41 weeks, with over 50% of singleton pregnancies delivering during this interval. The average gestational duration is approximately 40 weeks, though natural variation is common and not clinically concerning unless accompanied by signs of fetal compromise or maternal comorbidity.

Clinical guidelines from major obstetric organizations—including the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO)—emphasize that routine induction before 39 weeks should be avoided in uncomplicated pregnancies. Accurate dating—ideally confirmed by first-trimester ultrasound—is essential to determine gestational age and guide timing of delivery decisions.