Estimated date of delivery

[4] 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.

Due date estimation basically follows two steps: According to American College of Obstetricians and Gynecologists, the main methods to calculate gestational age are:[7]

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.

[11] Naegele's rule is a standard way of calculating the due date for a pregnancy when assuming a gestational age of 280 days at childbirth.

The calculation method does not always result in 280 days because not all calendar months are the same length; it does not account for leap years.

Distribution of gestational age at childbirth among singleton live births, given both when gestational age is estimated by first trimester ultrasound and directly by last menstrual period. About 80% of childbirths occur between 37 and 41 weeks of gestational age, with a somewhat more narrow span when based on first trimester ultrasound. [ 11 ]