What is involved in calculating the estimated due date (EDD)?

Calculating the estimated due date (EDD) is primarily based on the first day of the last menstrual period (LMP). The most widely accepted method involves adding 280 days, or 40 weeks, to the first day of the last menstrual period. This method is grounded in the typical 28-day menstrual cycle, during which ovulation usually occurs around two weeks after the start of the cycle. By using the LMP as a reference point, healthcare providers can estimate the EDD, ensuring that they account for the average duration of pregnancy.

This approach is commonly utilized in prenatal care because it provides a standardized and reliable method for estimating the progression of pregnancy and scheduling important prenatal assessments. While other methods may incorporate different data points, the calculation beginning with the LMP remains the cornerstone of determining the EDD in obstetric practice.