The phrase identifies a method, often associated with early pregnancy detection kits, of estimating the expected date of childbirth. This estimation is commonly achieved by adding 280 days (40 weeks) to the first day of the last menstrual period. For instance, if the last menstrual period began on January 1st, the estimated delivery date would be October 8th of the same year.
Such calculations provide expectant parents with a preliminary timeframe for preparing for the arrival of a child. This estimation aids in planning prenatal care appointments, making necessary lifestyle adjustments, and managing expectations regarding the pregnancy timeline. Historically, estimations of this nature have been vital in midwifery and obstetrics for monitoring fetal development and anticipating potential complications.