Understanding Nagele's Rule for Due Dates

Mar 12, 2025

Lecture on Nagele's Rule

Introduction

  • Presenter: Sarth
  • Occupation: Registered Nurse
  • Context: Part of an NCLEX review series on maternity nursing.
  • Additional Resources: Quiz available in the YouTube description to test understanding of Nagele's Rule.

What is Nagele's Rule?

  • Purpose: Used to estimate the due date of a baby.
  • Based on:
    • The woman's last menstrual period (LMP).
    • Assumes a 28-day menstrual cycle.
    • Typical gestation period of 280 days (40 weeks).
  • Note: It is an estimation because cycle lengths can vary and first-time mothers may go over 40 weeks.

Important Considerations

  • Months with 30 vs. 31 Days:
    • Remember the mnemonic: "30 days hath September, April, June, and November. All the rest have 31 except February alone."
    • February always considered as 28 days for simplicity.

Calculation Formulas for Nagele's Rule

  • Formula 1:
    • Subtract 3 months from LMP.
    • Add 7 days to the LMP.
    • Add 1 year.
    • Use for LMP from April to December.
  • Formula 2:
    • Add 7 days to the LMP.
    • Add 9 months.
    • Use for LMP from January to March.

Calculation Examples

Example 1: Easy Calculation

  • Scenario: LMP is September 2, 2016.
  • Steps:
    1. Subtract 3 months: June 2, 2016.
    2. Add 7 days: June 9, 2016.
    3. Add 1 year: June 9, 2017.
  • Estimated Due Date: June 9, 2017.

Example 2: Tricky Calculation

  • Scenario: LMP is September 28, 2016.
  • Steps:
    1. Subtract 3 months: June 28, 2016.
    2. Add 7 days: July 5, 2016 (because June has only 30 days).
    3. Add 1 year: July 5, 2017.
  • Estimated Due Date: July 5, 2017.

Incorrect Use of Formula 2

  • Mistake: Using Formula 2 for April to December LMPs.
  • Example Correction:
    • Adding 7 days to September 28 gives October 5, 2016.
    • Adding 9 months gives July 5.
    • Must remember to change the year to 2017.

Conclusion

  • Practice: Visit the website registerednursern.com for practice questions.
  • Additional Resources: Explore more videos in the NCLEX review series.
  • Call to Action: Consider subscribing to the channel for more content.

Full transcript