For practicing obstetricians and pediatricians, accurate gestational age (GA) is a cornerstone of quality care during pregnancy and the newborn period. GA determines prenatal management decisions, such as eligibility for antenatal glucocorticoids if preterm delivery is anticipated or timing of delivery in complicated pregnancies to avoid stillbirth or maternal morbidity. Knowledge of GA for women in labor also allows for transfer to facilities capable of handling preterm infants and guides postnatal resuscitation practices and specialized newborn care.