Ultrasound Based Redating of a Normal Pregnancy Without Maternal OR Fetal Abnormality

NOTE: Third Trimester Ultrasound Based Due Date is Least Reliable and Requires Follow Up of Interval Growth.

Step 1. Calculate GA/EDD by LMP here.

Step 2. Calculate GA/EDD by FIRST ULTRASOUND here.

Step 3. Use the GA/EDD by US if the discrepancy between ultrasound dating and LMP is:

  • Greater than 5 days before 9 0/7 weeks of gestation by LMP

  • Greater than 7 days from 9 0/7 weeks to 15 6/7 weeks by LMP

  • Greater than 10 days from 16 0/7 weeks to 21 6/7 weeks by LMP

  • Greater than 14 days from 22 0/7 weeks to 27 6/7 weeks by LMP

  • Greater than 21 days after 28 0/7 weeks by LMP

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Pregnancy Due Date Calculator

https://perinatology.com/calculators/Due-Date.htm 

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Calculate Due Date From US Report

https://www.perinatology.com/calculators/EDDSono.htm 

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Gestational Age on a Given Date for Induction of Labor OR C-Section

https://perinatology.com/Reference/Fetal%20development.htm 

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Gestational Age from Ultrasound Measurements

https://perinatology.com/calculators/Estimation%20of%20Fetal%20Weight%20and%20Age.htm#AGECALC 

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Pregnancy Wheel

https://www.prokerala.com/health/pregnancy/pregnancy-wheel/ 

First Trimester of Pregnancy: Less than14 weeks 0 days

Second Trimester of Pregnancy 14 weeks and 0 days through 27 weeks and 6 days

Third Trimester of Pregnancy 28 weeks 0 days through delivery

References: https://app.box.com/s/n14psxhkvo5owj4utbbbah92dc4gxl6l