Introduction
Generally, pregnancy lasts for around 280 days, that is 40 weeks. And, when a woman gets pregnant, the first day of the pregnancy is calculated from the first day of the last menstrual period. The last menstrual period is called LMP, even though the woman was not pregnant during that time, it is considered the first day of the pregnancy. As the baby's development in the womb lapses two weeks behind, the doctor takes two weeks early to compensate for the lapses.
What Is EDD and What Are Its Importance?
EDD is the estimated due date of delivery in pregnancy. It is the expected delivery date when the baby will come out from the womb of the mother. It is the date by which the doctor keeps a check on the gestational period.
The EDD of pregnancy is required because it provides the count of women's trimester and fetal development according to the ongoing trimester. There are three trimesters in pregnancy. The first trimester is from weeks 0 to 12; the second trimester is from weeks 13 to 26; the third trimester is from weeks 27 to 40.
How to Calculate EDD of Pregnancy?
The EDD of pregnancy is calculated in three ways, but the condition of the pregnant woman should have a regular menstrual period gap of 28 to 30 days. The three methods are:
-
Naegele's Rule - Naegele’s rule calculates the EDD of pregnancy by adding an extra seven days to the last menstrual period date (LMP) and subtracting the three months from it. Examples of Naegele's rule include taking the last menstrual period date (LMP) as December 1, 2022. Further adding extra seven days, making it December 8, 2022. Then subtract three months from it, making it September 8, 2023. It is the estimated due date (EDD) from the LMP.
-
Pregnancy Wheel - Another way of calculating the EDD is by the pregnancy wheel. It is the method usually used by the doctor to calculate EDD. It is easy to calculate the EDD using this method. The first step of calculating EDD in the pregnancy wheel is by defining the last menstrual period (LMP) date; after lining the LMP date in the pregnancy wheel with the indicator, it will present the EDD (estimated due date) itself. In cases of long menstrual periods and irregular periods, the doctor uses the pregnancy wheel accuracy to evaluate the estimated due dates (EDD).
-
EDD Calculators - Nowadays, the patient can calculate the EDD by typing the last menstrual period date (LMP) on the calculator presented online to calculate the EDD. One such calculator is on the iCliniq site, a virtual hospital providing patients with accurate EDD.
Is It Essential to Know the LMP of Women?
Yes, it is essential to know the woman's last menstrual period date (LMP) to calculate EDD, as, without the LMP, the estimated due date (EDD) cannot be calculated. However, if the patient has not kept track of the exact last menstrual period date, they can consider the week they had their last menstrual period. Or if the patient is entirely unknown of the previous periods, then ultrasounds are the most accurate and more reliable options for the due dates.
Which LMP Will be Taken for Irregular Periods Patients or Long Cycles Patients?
The menstrual period cycle is different for every woman, some have long cycles of more than 28 days, and some have irregular cycles. Generally, the second half of the menstrual cycle is 14 days only. During these 14 days, the woman ovulates for the next menstrual cycle. In these rare and long-cycle cases, the ovulating period is the last menstrual period (LMP). For example, in cases of long menstrual periods, as the patient encounters 35 days of the menstrual cycle, and the last menstrual period (LMP) was December 1, then add 21 days to it, making it December 22, then subtract 14 days (December 8) further to find the nearby last menstrual period date (LMP) that is December 8. After getting an LMP, use the pregnancy wheel date to calculate the estimated due date (EDD).
Why EDD Varies According to Doctors and Ultrasounds?
The estimated due dates (EDD) sometimes vary on each ultrasound, and even the EDD is given by the doctor also varies. All this is because the doctor estimates the EDD based on the LMP provided by the patient, and the ultrasound provides reports according to the fetal development in the womb. Both these dates are usually different. Although the doctor defines dates for fetal age, ultrasound defines fetal growth.
Is It Possible that EDD Can Change?
Yes, it is possible that the doctor can change the estimated due dates of the patient after diagnosing the fetal age. It usually occurs in cases where irregular periods occur, the patient has no specific last menstrual period date (LMP), or the doctor diagnoses the fetal size as smaller or larger. However, the changes are mainly in the first trimester when the first ultrasound depicts the estimated due date.
How Accurate Are the EDD After Calculating It By the Last Menstrual Period?
Estimated due dates are only sometimes accurate when calculated by the LMP. This is because only a few deliveries occur on the given EDD; the remaining deliveries usually occur before EDD and some after the due dates.
Is the EDD Different in All Three Trimesters?
The EDD encountered from the ultrasounds can vary from one trimester to another. But the most accurate is in the first trimester of the pregnancy, followed by the second trimester, which is less accurate than the first. Finally, the third-trimester outcomes are the most inaccurate, as different ultrasounds provide different results.
Conclusion
The EDD is the estimated due date provided by the doctor after considering the first day of the last menstrual period (LMP). The last menstrual period is essential to calculate the estimated due dates and in cases where LMP is not defined, like in irregular period cycles; the LMP is taken near the day of ovulation. There are two different methods of calculating the estimated due date (EDD). One is Naegele's rule, and the other is the pregnancy wheel. Among these, the pregnancy wheel is usually taken into account by doctors to calculate it. However, given the difference in the methods of calculating the EDD, doctors finally follow the EDD estimated by the ultrasound for a safe and sound delivery of the baby.
