What is the best method for determining the estimated due date?

Naegele's Rule is a widely used method for calculating the estimated due date (EDD) based on a woman’s last menstrual period (LMP). This rule provides a straightforward formula: you take the first day of the last menstrual period, add one year, subtract three months, and finally add seven days to arrive at the estimated due date. This method is simple and effective for women whose menstrual cycles are regular and typically 28 days long.

While ultrasound measurement is considered a reliable method for confirming gestational age, especially in the case of uncertain dates or irregular cycles, it is generally used as a follow-up to Naegele's Rule rather than the primary method of calculating an EDD. Similarly, calculating based on the last menstrual period can be slightly less reliable due to variations in cycle lengths or inaccuracies in reporting dates but serves as foundational knowledge for understanding Naegele's Rule.

Fetal heart rate monitoring is important for assessing the fetus's well-being during pregnancy and labor, but it does not provide any information regarding the due date. Thus, Naegele's Rule remains the best method for estimating the due date, particularly in the early stages of pregnancy when accurate dating is essential for prenatal care.