How to Calculate Gestational Age
What is Gestational Age?
Gestational age is pregnancy duration from last menstrual period. It's critical for fetal development assessment and delivery timing.
Step-by-Step Guide
- 1Naegele's rule: Add 7 days to LMP, then add 9 months
- 2Or: LMP + 280 days ≈ EDC
- 3Verify with first-trimester ultrasound for accuracy
Worked Examples
Input
LMP January 1
Result
EDC ≈ October 8 (280 days later)
Average pregnancy duration
Common Mistakes to Avoid
- ✕Using conception date instead of LMP
- ✕Ignoring ultrasound confirmation of dates
Frequently Asked Questions
Why measure gestational age precisely?
Guides timing for pregnancy care, delivery decisions, neonatal viability judgments.
Is Naegele's rule always accurate?
Accurate ±2 weeks for first trimester dating. Less accurate with irregular cycles or uncertain LMP.
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