Pregnancy is a magical milestone that happens in a woman’s life where a baby is carried inside her womb for nine months. A full-term pregnancy continues for a period of 40 weeks, or 280 days. And EDD can be calculated from the first day of LMP (last menstrual period).
Expected Date Of Delivery is a term frequently used by doctor’s stands for expected date of delivery or estimated date of delivery for your baby. Generally, EDD can be calculated by adding 280 days to the first day of the last menstrual period of a woman.
Calculation Of The Expected Date Of Delivery
There are several ways to calculate the expected date of delivery. Here I mentioned one of them to easily calculate your EDD.
To ascertain the date upon which childbirth should take place, add the number of the day of the month on which the last menstruation occurred to the date in the following table, placed in italics after the months concerned.
| Months in which menstruation occured | Add day of month to | Months in which menstruation occured | Add day of month to |
|---|---|---|---|
| January | October 7 | July | April 6 |
| February | November 7 | August | May 7 |
| March | December 5 | September | June 7 |
| April | January 5 | October | July 7 |
| May | February 5 | November | August 7 |
| June | March 7 | December | September 6 |
Example:If menstruation last occurred on December 17,add 17 to Septmber 6 and confinement should take place on september 13.
Other Methods of Calculating EDD
Naegele’s Rule
Naegele’s Rule is one of the most commonly used methods for calculating the EDD. According to this rule 280 days (40 weeks) to the start of the last menstrual period (LMP). This method assumes a 28-day menstrual cycle with ovulation occurring on the 14th day.
Formula: LMP + 7 days – 3 months + 1 year
For example, if the LMP is January 1, 2024:
Add 7 days: January 8, 2024
Subtract 3 months: October 8, 2023
Add 1 year: October 8, 2024
Thus, the EDD is October 8, 2024.
Ultrasound Scan
Ultrasound scans provide a more accurate EDD, especially when performed in the first trimester. Measurements of the embryo or fetus, such as the crown-rump length (CRL), can estimate gestational age and, subsequently, the EDD. Ultrasounds are particularly useful for women with irregular menstrual cycles or uncertain LMP dates.
Pregnancy Wheel
A pregnancy wheel, also known as a gestation calculator, is a simple tool used by healthcare providers. It consists of a circular calendar with dates marked on the outer edge and weeks of gestation on the inner edge. By aligning the LMP with the appropriate marker, the wheel indicates the EDD.
Conception Date
If you know the exact conception date, you can calculate the EDD by adding 266 days (38 weeks) to it. This method is less commonly used as pinpointing the exact day of conception can be challenging.
Factors Influencing EDD Accuracy
Several factors can influence the accuracy of the EDD, including:
- Menstrual Cycle Variability: Women with irregular cycles may find it difficult to determine their LMP accurately.
- Ovulation Timing: Ovulation does not always occur on the 14th day of the cycle.
- Embryo/Fetal Growth Variability: Individual differences in growth rates can affect ultrasound measurements.
- Multiple Pregnancies: Twins or multiples often have different growth patterns and may be delivered earlier than single pregnancies.
Importance of EDD in Prenatal Care
Accurate EDD calculation is vital for:
- Monitoring Fetal Development: Healthcare providers use the EDD to track the growth and development of the fetus, ensuring it aligns with standard milestones.
- Planning Prenatal Visits: Regular check-ups and screenings are scheduled based on gestational age to monitor the health of both the mother and the fetus.
- Preparing for Childbirth: Knowing the EDD helps expectant parents and healthcare providers prepare for labor and delivery, including making necessary arrangements and decisions about the birthing plan.
What is LMP and why is it important for pregnancy?
LMP (last menstrual period) refers to the first day of a woman’s last menstrual period. It is important to calculate the estimate due date, or EDD.
Due to irregular periods, the delivery can occur at any time between 37 and 42 weeks. And through ultra-sound, the gestational age can be confirmed by the doctor.
Factors influencing changes in the due date of delivery
A full-term pregnancy usually occurs between 40 and 41 weeks. While only 30 per cent of pregnancies continue until the 40th week, most deliveries are done in-between the 38th and 39th weeks. Factors influencing the due date are mentioned below:
- If embryos took longer time to implant and grow during the pregnancy period.
- Hormones related to the process of pregnancy may have a significant effect on the due date.
- Women who were heavier at birth may have had longer gestation.
- Women’s with irregular periods.
- The foetal heartbeat, fundamental height, and the first time the baby moves all have an impact on the due date.
In this video, the doctor explains a most accurate way to calculate the delivery date.
FAQ’s
Can my estimated due date change?
Yes,your EDD can change,but you need not to be worried. In general, it doesn’t happen a lot. But the date can be changed due to various factors.
When should you take a pregnancy test?
The best period to test for pregnancy is one week after a missed period.
How accurate are the home pregnancy kits?
Home pregnancy test kits are quite accurate as they detect the presence of hCG (human chronic gonadotropin)in urine.
Conclusion
Women having regular periods and knowing their LMP date can easily calculate their EDD or estimated due date by 280 days, or 9 months and 7 days to the first day of their last menstrual period, i.e., LMP.
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Also read:
Reference:
- D.A.SAVANT,The pharmaceutical sciences-Pharma pathway,pg-5.18
- Calculating a due date. http://www.hopkinsmedicine.org/healthlibrary/conditions/pregnancy_and_childbirth/calculating_a_due_date_85,P01209/
- Calculating your estimated due date. https://my.clevelandclinic.org/health/diseases_conditions/hic_Am_I_Pregnant/hic_Calculating_Your_Estimated_Due_Date
- Due date calculator. (n.d.). http://www.marchofdimes.org/pregnancy/calculating-your-due-date.aspx
- Pregnancy due date and gestational age calculator. http://www.perinatology.com/calculators/Due-Date.htm
- ACOG reinvents the pregnancy wheel: Launches new due date app. https://www.acog.org/About-ACOG/News-Room/News-Releases/2016/ACOG-Reinvents-the-Pregnancy-Wheel
