Frieds Rule Calculator

Frieds Rule Calculator calculator can be used to estimate the size of an embryo or fetus based on maternal measurements during pregnancy. It's commonly used in early pregnancy ultrasounds to estimate gestational age.

Input Parameters

If not available, leave blank

If not available, leave blank

Calculation Results

Estimated Gestational Age

Enter input values and click Calculate to see results

Calculation Formula

GA (days) = 280 + 2.31 * CRL (cm) - 4.73

Where:
GA = Gestational Age in days
CRL = Crown-Rump Length in centimeters
This formula is based on measurements typically taken in the first trimester (up to 14 weeks).

Frieds Rule Calculator Calculator Usage Guide

Learn how to use the Frieds Rule Calculator and understand its clinical applications

How to Use This Calculator

  1. Enter the Crown-Rump Length (CRL) of the fetus in centimeters. This is the most important measurement for Frieds Rule and should be obtained from a crown-rump length ultrasound.
  2. If available, enter the Fetal Breech Length (BRL) to obtain an alternative estimate. This is particularly useful if the CRL measurement is difficult to obtain accurately.
  3. If you have a prior gestational age estimate, you can enter it to compare with the calculated value.
  4. Click the "Calculate" button to compute the estimated gestational age in days.
  5. The calculator will display the estimated gestational age based on CRL, and if BRL is provided, it will show an alternative estimate.

Clinical Applications

Frieds Rule is particularly useful in early pregnancy when determining the gestational age of a fetus. It's commonly used when:

  • The last menstrual period (LMP) is uncertain or unknown
  • First-trimester ultrasound is performed to confirm viability and estimate gestational age
  • There is need to assess fetal development relative to gestational age

Limitations and Considerations

This calculator provides an estimate based on the Frieds Rule formula, which has some limitations:

  • The accuracy of Frieds Rule depends on accurate measurement of CRL or BRL
  • This formula is most accurate between 6-14 weeks of gestation
  • For later gestations, other methods of estimating gestational age may be more appropriate
  • The calculator does not account for individual variations in fetal growth patterns

Note: This calculator should be used as an aid to clinical judgment and not as a standalone diagnostic tool. Always consult with a healthcare provider for pregnancy management decisions.