1. What is NSW Health EDD Calculator?

The NSW Health Estimated Due Date (EDD) calculator determines the expected delivery date based on the last menstrual period (LMP) using the standard formula of LMP plus 280 days (40 weeks).

2. How Does the Calculator Work?

The calculator uses the NSW Health EDD formula:

Where:

• \( EDD \) — Estimated Due Date
• \( LMP \) — Last Menstrual Period
• \( 280 \text{ days} \) — Standard pregnancy duration (40 weeks)

Explanation: This calculation method is based on Naegele's rule and is widely used in clinical practice throughout NSW Health facilities.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for prenatal care planning, fetal growth monitoring, timing of prenatal tests, and preparing for delivery.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period in the date field. Ensure the date is accurate as this forms the basis for all subsequent pregnancy dating.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the LMP method?
A: The LMP method is generally accurate for women with regular 28-day cycles. Ultrasound dating may be used for confirmation, especially if cycles are irregular.

Q2: What if I don't know my LMP?
A: If LMP is unknown, an early pregnancy ultrasound (before 14 weeks) provides the most accurate due date estimation.

Q3: Why 280 days instead of 9 months?
A: Pregnancy is calculated as 40 weeks from LMP, which equals 280 days. This accounts for the fact that conception typically occurs about 2 weeks after LMP.

Q4: Are there other methods to calculate EDD?
A: Yes, ultrasound measurements (especially crown-rump length in first trimester) and conception date can also be used, but LMP remains the primary method.

Q5: What percentage of babies are born on their due date?
A: Only about 5% of babies are born exactly on their due date. Most births occur within 2 weeks before or after the estimated date.