How to calculate the due date
Disease description:
I've noticed in TV dramas that when women give birth, there's often mention of an estimated due date. How exactly is this estimated due date calculated?
Doctor's answer (1)
Dr. Zhang Lu
The estimated due date is calculated based on the first day of the last menstrual period. This method is known as "Naegele's rule" or the "last menstrual period method," and it is the most commonly used approach.
The specific calculation method is: add 9 to or subtract 3 from the month, and add 7 to the day. For example, if the first day of the last menstrual period was January 1, 2024, the estimated due date would be October 8, 2024, assuming the woman has a regular menstrual cycle.
In cases of irregular menstrual cycles, an ultrasound performed early in pregnancy—around seven weeks gestation—can visualize the fetal heartbeat and embryonic development, allowing for a more accurate estimation of gestational age. However, during the second trimester and beyond, the accuracy of ultrasound in estimating the due date may decrease due to greater variability in fetal growth.
The estimated due date can also be calculated based on the date of first fetal movement, basal body temperature curve, or the onset of morning sickness. However, these methods are generally less accurate than the aforementioned ones.
The estimated due date is only a reference value; the actual delivery date may occur earlier or later. If there are no signs of labor by the estimated due date, timely communication and consultation with a healthcare provider are recommended.
