Why do Pregnancy due dates change?

Pregnancy due dates can change due to various factors, primarily based on the accuracy of the initial dating. Due dates are typically calculated from the first day of the last menstrual period (LMP), but if a woman has irregular cycles or if conception occurs later than expected, the due date may be adjusted. Additionally, ultrasounds can provide a more accurate estimation of gestational age, leading to changes in the due date if the measurements differ from the LMP calculation. Ultimately, the goal is to ensure the best care and monitoring for both the mother and the baby.