How to Compute Age of Gestation

In this guide, we'll walk through how to compute the age of gestation (AOG) and expected delivery date (EDC) manually. Specialties Ob/Gyn Article

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How to Compute Age of Gestation

AOG refers to the length of time a fetus has been developing inside the mother's uterus. It is calculated in weeks and days, starting from the first day of the mother's last menstrual period (LMP).

The EDC, also known as the estimated due date (EDD), is the projected date when a pregnant woman is expected to give birth. Accurately estimating the EDC (estimated date calculator) helps healthcare professionals monitor the progress of pregnancy and plan appropriate care.

How to Compute AOG and EDC Manually

There are a few different methods and formulas for computing AOG and EDC manually, including Naegele's Rule, McDonald's Rule, and LMP-based calculations.

Naegele's Rule

Naegele's Rule is a standard method for estimating the EDC based on the mother's LMP. Follow these steps:

  1. Determine the first day of the LMP.
  2. Subtract 3 months.
  3. Add 7 days.
  4. Add 1 year.

Example: If the LMP is January 10, 2023:

  1. Subtract 3 months: October 10, 2022
  2. Add 7 days: October 17, 2022
  3. Add 1 year: October 17, 2023 (EDC)

McDonald's Rule

McDonald's Rule estimates AOG using fundal height (the distance between the pubic bone and the top of the uterus). Here's the steps:

  1. Measure fundal height in centimeters (cm).
  2. Divide the fundal height by 4.

Example: If the fundal height is 24 cm:

  • 24 cm ÷ 4 = 6 (AOG in months)

LMP-Based Calculations

To compute AOG using LMP (last menstrual period), follow these steps:

  1. Calculate the number of days between the current date and the first day of the LMP.
  2. Divide the total number of days by 7 to find the AOG in weeks.

Example: If the LMP is January 10, 2023, and the current date is June 10, 2023:

  1. Days between: 151
  2. 151 ÷ 7 ≈ 21.6 (AOG in weeks)
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Specializes in Vents, Telemetry, Home Care, Home infusion.

Naegles rule example is not correctly written as LMP 1/17/2023  would be born in 2023, not fall 2024.

Correction

Example: If the LMP is January 10, 2023:

    Subtract 3 months: October 10, 2022

    Add  7 days: October 17, 2022

    Add 1 year: October 17, 2023 (Estimated date calculator (EDC)

https://www.medcomic.com/medcomic/naegeles-rule/

https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date

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What is the AOG and EDD of the following:

With the date of check up which is July 27, 2021

LMP= July 10, 2021

LMP= February 26, 2021

LMP= November 30, 2021

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

We are happy to help with homework but as I have said each time I have helped you we will not do it for you. What is the length of the average human pregnancy?

If a pregnancy takes forty weeks......what is the Age of Gestation and Estimated Due Date according to these LMP dates.

Adding 4O weeks to the LMP of 06/10/2021 is.....

Adding 4O weeks to the LMP of 02/26/2021

Adding 4O weeks to the LMP of 11/30/2021

What are your answers?

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Specializes in PICU, Sedation/Radiology, PACU.

An easy way to calculate the EDD is Naegele's Rule: How to Compute Age of Gestation

By using some simple addition and subtraction, you can easily calculate the EDD.

As far as calculating the AOG at any certain date- get yourself a calendar and count the weeks.

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Yeah! These are my answers.

LMP: July 10, 2021

April 10, 2021(subtract 3 months)
April 17, 2021(add 7 days)
April 17, 2022 (add 1 year)

LMP: February 26, 2021

November 26, 2021(subtract 3 months)
December 3, 2021 (add 7 days)
December 3, 2022 (add 1 year)

LMP: November 30, 2021

August 30, 2021 (subtract 3 months)
September 6, 2021 (add 7 days)
September 6, 2022 (add 1 year)

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