1. What is the EDD Calculation?

The Estimated Due Date (EDD) calculation estimates the expected delivery date based on the Last Menstrual Period (LMP) with the standard formula of LMP + 280 days. The calculator can also adjust this estimate using Crown-Rump Length (CRL) measurements from early ultrasound.

2. How Does the Calculator Work?

The calculator uses the standard formula:

When CRL measurement is provided, it uses the Robinson formula:

Where:

• \( LMP \) — First day of last menstrual period
• \( CRL \) — Crown-rump length in millimeters
• \( 280 \text{ days} \) — Standard pregnancy duration (40 weeks)

Explanation: The standard calculation assumes a 28-day menstrual cycle with ovulation on day 14. CRL measurement provides more accurate dating in early pregnancy.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for appropriate prenatal care timing, monitoring fetal growth, planning delivery, and identifying preterm or post-term pregnancies.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period. For increased accuracy, provide CRL measurement from an early ultrasound (typically between 6-13 weeks gestation).

5. Frequently Asked Questions (FAQ)

Q1: Why is 280 days used for pregnancy calculation?
A: 280 days represents 40 weeks of gestation, calculated from the first day of the last menstrual period, which is the standard method used in obstetrics.

Q2: How accurate is CRL for dating pregnancy?
A: CRL measurement in early pregnancy (6-13 weeks) is the most accurate method for dating, with accuracy of ±5-7 days.

Q3: What if my cycle isn't 28 days?
A: The standard calculation assumes a 28-day cycle. Women with significantly longer or shorter cycles may need adjustment based on ovulation timing.

Q4: When should I get an ultrasound for dating?
A: First-trimester ultrasound between 6-13 weeks provides the most accurate dating. Later ultrasounds are less accurate for establishing due dates.

Q5: Can the due date change during pregnancy?
A: Yes, if early ultrasound dating differs significantly from LMP-based dating (typically more than 5-7 days), providers will usually adjust to the ultrasound date.