Waiting for the baby’s birth is both exciting and stressful for the parents-to-be. Getting to know the date of the baby’s arrival ahead of its birth helps to prepare the parents for childbirth. Doctors use different methods to calculate the due date or the estimated date of delivery (EDD). An EDD calculator is commonly used, which is accurate to a significant extent.
The EDD calculator helps in assessing the time of delivery, whether it is full term (40 weeks), pre term (before 37 weeks) and post term (beyond 40 weeks). In most cases deliveries occur 2 weeks before or after EDD with only 4% to 5% deliveries occurring on the estimated due date.
An EDD calculator online is a convenient tool available for quick calculations.
Two EDD calculating methods are generally used.
1. EDD calculator using LMP (last menstrual period)
This method makes use of parameters such as these:
One can calculate EDD using Naegele’s rule (manually) :add 7 days to the first day of LMP, add 1 year to the year of conception, and lastly subtract 3 months from the month of LMP.
This method is useful in case of women with regular monthly periods. The chances of errors in this method are very high when periods are irregular and also due to the inaccuracy or inability to recollect the exact date of the last menstrual period.
2. EDD calculator based on ultrasound findings.
Calculating EDD based on an ultrasound scan (USG) is more accurate than the LMP method.
In this method, EDD is calculated by measuring the size of the baby growing inside the womb. Different measurements used as reference parameters corresponding to the age of the fetus are used in determining EDD. The size of the baby is measured for the crown-rump length, biparietal diameter and femur length. These are used to measure the length and size of the head of the baby.
USG aids in calculating EDD in early pregnancy, up to 12 weeks. It is not useful in predicting the due date beyond the fifth month of pregnancy. USG also helps in finding out the gestational age or the length of pregnancy till date.
It is important to calculate and document EDD in the first trimester of pregnancy. Using both the LMP and USG methods is important to plan and manage pregnancy and delivery.
In some cases, there is a difference in the due date calculated using the LMP method and USG done in the second trimester of pregnancy. In such cases, the EDD is changed corresponding to the findings from the second trimester of USG.
Calculating EDD in case of a pregnancy resulting from assisted reproductive technology (ART) involves certain modifications with respect to the age of the embryo and duration of pregnancy.
In EDD calculator for IVF or in vitro fertilization, parameters such as the age of the embryo resulting from the artificial fertilization procedure and the date on which the products of artificial fertilization are transferred to the womb are considered.
Disclaimer: The information in the article is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your doctor.
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