IVF and FET Due Date Calculation
For pregnancies conceived through in vitro fertilization (IVF) or frozen embryo transfer (FET), due dates are calculated differently than natural conceptions. Since the exact date of embryo creation is known, the calculation is typically more precise.
How Does It Work?
The calculator first determines an "equivalent LMP" date, the date your last period would have started if you had conceived naturally. This is calculated as: Transfer date − (14 + embryo age in days). Then, 280 days are added to get the due date, just like Naegele's rule.
Day 3 vs Day 5 Embryos
Day 3 (cleavage stage): The embryo has been developing for 3 days since fertilization. The equivalent LMP is 17 days before transfer.
Day 5 (blastocyst): A more developed embryo, transferred 5 days after fertilization. The equivalent LMP is 19 days before transfer. Blastocyst transfers generally have higher implantation rates.
Important Notes
Your fertility specialist will confirm your due date with early ultrasound measurements. IVF due dates are generally considered very reliable because the timing of fertilization is precisely known. Follow your clinic's specific guidance for your pregnancy timeline.