Baby Due Date Calculator Fet

The First Embryonic Tissue (FET) method is a more precise way to calculate your due date compared to the traditional last menstrual period (LMP) method. This calculator helps you determine your estimated due date based on fetal development stages.

What is the FET method?

The FET method uses ultrasound measurements of the first embryonic tissue (FET) to determine fetal development. This method is considered more accurate than the traditional LMP method because it accounts for variations in menstrual cycle length.

The FET measurement is taken when the embryo is between 5.5 and 6.5 days old, which corresponds to about 5-6 weeks of pregnancy. The measurement is taken from the crown to the rump of the embryo.

The FET method is typically used when there are concerns about the accuracy of the LMP method, such as irregular menstrual cycles or a history of miscarriage.

How to use this calculator

To use this calculator, you'll need to know the date of your first day of your last menstrual period (LMP) and the FET measurement in millimeters. Enter these values into the calculator and click "Calculate" to determine your estimated due date.

The calculator will display your estimated due date based on the FET method, as well as a comparison with the traditional LMP method.

Formula used

The FET method uses the following formula to calculate the estimated due date:

Estimated Due Date = LMP Date + (FET Measurement - 5.5) × 2.5 days

Where:

LMP Date is the first day of your last menstrual period
FET Measurement is the length of the first embryonic tissue in millimeters

This formula accounts for the fact that the embryo grows at a rate of approximately 2.5 days per millimeter of FET measurement.

Worked example

Let's say you had your last menstrual period on January 1, 2023, and your FET measurement was 6.2 mm. Using the formula:

Estimated Due Date = January 1, 2023 + (6.2 - 5.5) × 2.5 days

= January 1, 2023 + 0.7 × 2.5 days

= January 1, 2023 + 1.75 days

= January 3, 2023

Therefore, your estimated due date would be January 3, 2023.

FAQ

What is the difference between the FET method and the LMP method?

The FET method uses ultrasound measurements of fetal development to calculate the due date, while the LMP method uses the first day of your last menstrual period. The FET method is considered more accurate because it accounts for variations in menstrual cycle length.

When should I use the FET method?

The FET method is typically used when there are concerns about the accuracy of the LMP method, such as irregular menstrual cycles or a history of miscarriage.

Is the FET method more accurate than the LMP method?

Yes, the FET method is generally considered more accurate than the LMP method because it accounts for variations in menstrual cycle length and fetal development.

Can I use this calculator for a pregnancy that has already started?

Yes, you can use this calculator for any pregnancy, regardless of how far along it is. Simply enter the date of your last menstrual period and the FET measurement to get an accurate estimate of your due date.