The duration of pregnancy is between 280 and 290 days from the first day of the last menstrual period and varies according to the literature, the authors, the calculation methods and the characteristics of women. Assuming that the date of beginning of pregnancy is known, the expected date of delivery varies depending on the length of gestation. Thus, in literature and in obstetric practice, there is no consensus on the definition of expected date of delivery. From a medical point of view, it seems important to fix the date from which the monitoring should start and from which an induction of labour should be considered. Thus, arbitrarily, we can consider that the term period corresponds to a time interval located between 37(+0) SA and 41(+6) SA and the post-term period begins from 42(+0) SA. Because maternal and fetal risks increase at the end of the pregnancy, one can speak, arbitrarily, of prolonged pregnancy from 41(+0) SA (expert opinion).