1. What is the Lister Pregnancy Calculator?

The Lister Pregnancy Calculator estimates the due date (EDD) based on the last menstrual period (LMP) using the standard formula of LMP + 280 days. This method is widely used in obstetrics for pregnancy dating.

2. How Does the Calculator Work?

The calculator uses the Lister formula:

Where:

• \( EDD \) — Estimated Due Date
• \( LMP \) — Last Menstrual Period
• \( 280 \) — Standard pregnancy duration in days

Explanation: This calculation assumes a 40-week pregnancy duration from the first day of the last menstrual period, which is the standard method used in clinical practice.

3. Importance of EDD Calculation

Details: Accurate due date estimation is crucial for monitoring fetal development, scheduling prenatal care, determining gestational age, and planning for delivery.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period in the date field. The calculator will automatically compute your estimated due date based on the standard 280-day pregnancy duration.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the Lister EDD calculation?
A: The Lister method provides a good estimate, but actual delivery dates can vary. Only about 5% of women deliver exactly on their EDD.

Q2: What if I don't know my LMP?
A: If LMP is unknown, an ultrasound in the first trimester can provide a more accurate due date estimation based on fetal measurements.

Q3: Why 280 days instead of 9 months?
A: 280 days equals 40 weeks, which is the standard medical calculation. Calendar months vary in length, so weeks provide more consistent measurement.

Q4: Does this work for irregular cycles?
A: The calculation assumes a regular 28-day cycle. Women with irregular cycles may need ultrasound dating for accuracy.

Q5: When should I confirm with healthcare provider?
A: Always confirm your due date with your healthcare provider, who may adjust it based on ultrasound findings and clinical assessment.