Understanding Your Frozen Embryo Transfer (FET) Due Date
Calculating the estimated due date (EDD) after a Frozen Embryo Transfer (FET) involves a few key pieces of information. Unlike natural conception or fresh embryo transfers, FETs require accounting for the specific development stage of the embryo at the time of transfer and the established medical guidelines for pregnancy dating.
How the Calculation Works:
The standard method for calculating a due date from an FET is to determine the total estimated gestational age (typically 40 weeks from the Last Menstrual Period, or LMP) and then add that to the date of the transfer, adjusted by the embryo's age and the gestational age already achieved at transfer.
Our calculator uses the following logic:
Reference Point: The FET date is your primary input.
Gestational Age at Transfer: We need to know how many weeks and days of pregnancy had already passed when the embryo was transferred. This is crucial because the embryo has already "been developing" in terms of gestational dating.
A 3-day embryo transferred means the gestational age is typically considered 3 days less than if conception occurred naturally on the transfer date.
A 5-day (blastocyst) embryo transferred means the gestational age is typically considered 5 days less.
Total Gestational Age: A full-term pregnancy is generally considered 40 weeks (280 days) from the LMP. For FET, we aim to reach approximately 40 weeks from the *implied* LMP, which is often around 38 weeks from the estimated ovulation/conception date.
Calculation Simplified:
Calculate the total days of pregnancy from the implied LMP to the target 40 weeks.
Calculate the days of pregnancy that had already passed at the time of FET (Weeks x 7 + Days).
Subtract the days of pregnancy already passed from the total pregnancy days to find the remaining days until the EDD.
Add these remaining days to the FET date to arrive at the EDD.
Formula Used: Days Remaining = (40 weeks * 7 days/week) - (Gestational Age at Transfer in Days) Estimated Due Date = FET Date + Days Remaining
*Note: The "Embryo Age at Transfer (Days)" input helps refine the understanding of Gestational Age at Transfer. For simplicity and standard clinical practice, the calculator directly uses the provided Gestational Age at Transfer (Weeks + Days) which inherently accounts for the embryo's stage.*
Example Scenario:
Let's say your Frozen Embryo Transfer (FET) occurred on October 15, 2023.
You transferred a 5-day embryo.
The clinical dating indicated you were approximately 5 weeks and 2 days pregnant at the time of transfer.
FET Date: October 15, 2023
Gestational Age at Transfer: 5 weeks and 2 days = (5 * 7) + 2 = 37 days
Embryo Age: 5 (This field is informational, the calculation relies on Gestational Age)
Gestational Age at Transfer: 5 weeks, 2 days
The resulting estimated due date would be June 14, 2024.
Important Considerations:
This calculator provides an estimated due date. Actual delivery dates can vary.
Always confirm your due date with your fertility clinic and healthcare provider. They use specific protocols and may account for additional factors.
The "Embryo Age at Transfer" field is often correlated with the "Gestational Age at Transfer." For example, a 5-day blastocyst is typically transferred around 5 weeks gestational age. The calculator prioritizes the explicit "Gestational Age at Transfer" input for precision.
function calculateDueDate() {
var fetDateInput = document.getElementById("fetDate");
var embryoAgeInput = document.getElementById("embryoAge");
var gestationalWeeksInput = document.getElementById("gestationalWeeks");
var gestationalDaysInput = document.getElementById("gestationalDays");
var resultDiv = document.getElementById("result");
// Clear previous results
resultDiv.innerHTML = ";
var fetDateStr = fetDateInput.value;
var embryoAge = parseInt(embryoAgeInput.value);
var gestationalWeeks = parseInt(gestationalWeeksInput.value);
var gestationalDays = parseInt(gestationalDaysInput.value);
// — Input Validation —
if (!fetDateStr) {
resultDiv.innerHTML = 'Please enter the Frozen Embryo Transfer date.';
return;
}
if (isNaN(gestationalWeeks) || isNaN(gestationalDays)) {
resultDiv.innerHTML = 'Please enter valid Gestational Age at Transfer (weeks and days).';
return;
}
if (gestationalDays 6) {
resultDiv.innerHTML = 'Gestational Age days must be between 0 and 6.';
return;
}
// Embryo age is informational, not strictly required for this calculation method but good to have a sanity check
if (isNaN(embryoAge) || embryoAge < 0) {
// Optionally warn the user, but proceed if gestational age is valid
// console.warn("Embryo Age is invalid or missing.");
}
// — Calculation Logic —
var fetDate = new Date(fetDateStr);
// Ensure the date is valid
if (isNaN(fetDate.getTime())) {
resultDiv.innerHTML = 'Invalid Frozen Embryo Transfer date entered.';
return;
}
// Calculate total gestational days at transfer
var totalGestationalDaysAtTransfer = (gestationalWeeks * 7) + gestationalDays;
// Standard full term is 40 weeks (280 days) from LMP.
// For FET, we often consider 38 weeks from conception/transfer date to reach term.
// Let's use the standard 40 weeks from implied LMP, and add remaining days to FET date.
// Total desired pregnancy duration in days (from LMP to 40 weeks)
var totalPregnancyDurationDays = 40 * 7; // 280 days
// Days remaining from FET date to reach 40 weeks from implied LMP
var daysRemaining = totalPregnancyDurationDays – totalGestationalDaysAtTransfer;
// Calculate the Estimated Due Date
var dueDate = new Date(fetDate);
dueDate.setDate(fetDate.getDate() + daysRemaining);
// Format the due date for display
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedDueDate = dueDate.toLocaleDateString(undefined, options);
// Display the result
resultDiv.innerHTML = 'Estimated Due Date: ' + formattedDueDate + '';
}