Concept
The estimated date of delivery (EDD), also known as expected date of confinement, and estimated due date or simply due date, is a term describing the estimated delivery date for a pregnant person. Normal pregnancies last between 38 and 42 weeks. Children are delivered on their expected due date about 4% of the time. Confinement is a traditional term referring to the period of pregnancy when an upper-class, noble, or royal woman would withdraw from society in medieval and Tudor times and be confined to their rooms with midwives, ladies-in-waiting and female family members only to attend them. This was believed to calm the mother and reduce the risk of premature delivery. "Lying-in" or bedrest is no longer a part of antenatal care. Due date estimation basically follows two steps: Determination of which time point is to be used as the origin for gestational age. This starting point is the person's last normal menstrual period (LMP) or the corresponding time as estimated by a more accurate method if available. Such methods include adding 14 days to a known duration since fertilization (as is possible in in vitro fertilization) or by obstetric ultrasonography. Adding the estimated gestational age at childbirth to the above time point. Childbirth on average occurs at a gestational age of 280 days (40 weeks), which is therefore often used as a standard estimation for individual pregnancies. However, alternative durations as well as more individualized methods have also been suggested. Gestational age According to American Congress of Obstetricians and Gynecologists, the main methods to calculate gestational age are: Directly calculating the days since the beginning of the last menstrual period Early obstetric ultrasound, comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age (such as calculated from last menstrual periods), and using the mean gestational age of other embryos or fetuses of the same size.