A Common Language: What Exactly Does 34 Weeks Gestation Mean?

There are multiple conventions for gestational age notation, which lead to different interpretations of completed weeks. This variability is exemplified by the different gestational age ranges recommended for administration of antenatal corticosteroid prophylaxis. Antenatal corticosteroid prophylaxis is widely recommended for women at risk of preterm delivery up to 34 completed weeks gestation. According to the World Health Organization, 34 completed weeks refers to the time period from the first day of the last menstrual period (day zero) to 34 weeks and 6 days of gestation (i.e., to 34⁺⁶ 34 weeks, or 244 days gestation). However, an alternative convention interprets 34 completed weeks as the period from the first day of the last menstrual period to 33⁺⁶ 36 weeks' gestation (i.e., 237 days' gestation). These inconsistencies in gestational age notation may have led to different practice recommendations for antenatal corticosteroid prophylaxis worldwide. Agreeing on the World Health Organization notation and interpretation of completed weeks may help promote clear communication within our discipline and more precise and effective knowledge dissemination.