Due-date calculation (Naegele’s rule)

$$ LMP -3 mon + 7 dy + 1yr $$

https://www.mdcalc.com/calc/423/pregnancy-due-dates-calculator

1. Identify the first day of your last menstrual period (LMP).
2. Subtract 3 months from that date.
3. Add 7 days to that date.
4. Add 1 year.

*Less reliable with irregular cycle (> 5 dy difference in cycle length)

• Alternatives:
  • IVF date
  • T1 dating ultrasound (fetal size) +/- 5 dy

Timeline

Pregnancy Timeline

• LMP: First day of the last menstrual period
• EDB: Estimated date of birth (3% actually deliver on due date)
  • Pre-term: < 37 wk
  • Term: 37-42 wk
  • Post-date: 41 wks → IOL - Induction of Labour, Post-date surveilance
  • Post-term: >42 wk → mobility/mortality and operative delivery rate starts increasing
  • Average duration: 280 days (40 wks +/- 17 days)
• GTPAL System

Trimesters

Calculators

GA → Date Calculator

LMP → Due Date Calculator