Fresh vs. Frozen Transfer Due Dates

The Quick Answer

No, fresh and frozen embryo transfers use the same due date formula.

Whether your embryo was transferred fresh (during your stimulation cycle) or frozen and transferred later (FET), the calculation depends only on:

1. Your transfer date
2. The embryo's age at transfer (day 3, 5, or 6)

The formula for both:

Now let's explore why this is the case and what actually differs between fresh and frozen transfers.

Understanding Fresh Embryo Transfers

In a fresh transfer cycle, embryos are transferred during the same menstrual cycle as egg retrieval. The typical timeline looks like this:

• Day 0: Egg retrieval and fertilization
• Days 1-5/6: Embryo development in the lab
• Day 3, 5, or 6: Embryo transfer

Fresh transfers happen quickly—usually within a week of egg retrieval. The embryo never leaves the laboratory environment between fertilization and transfer.

When Fresh Transfers Are Used

Fresh transfers may be chosen when:

• There's no risk of ovarian hyperstimulation syndrome (OHSS)
• The uterine lining develops well during stimulation
• No preimplantation genetic testing is needed
• The patient prefers not to wait for a FET cycle
• Clinic protocols favor fresh transfers in certain situations

Understanding Frozen Embryo Transfers (FET)

In a frozen embryo transfer, embryos are cryopreserved (frozen) after reaching the desired developmental stage and transferred in a later cycle. The timeline is different:

• Day 0: Egg retrieval and fertilization
• Days 1-5/6: Embryo development in the lab
• Day 5 or 6: Embryo freezing (vitrification)
• Weeks to years later: FET cycle begins
• FET day: Embryo thawed and transferred

The embryo could be frozen for a few weeks or many years—vitrification effectively stops biological time for the embryo.

When Frozen Transfers Are Used

FET has become increasingly common and is now the most frequent type of transfer in many clinics. Reasons include:

• Freeze-all protocols: Some clinics routinely freeze all embryos to allow the body to recover from stimulation before transfer
• OHSS prevention: High responders at risk for ovarian hyperstimulation benefit from frozen cycles
• PGT-A/PGT-M testing: Genetic testing requires time to get results, necessitating freezing
• Elective reasons: Scheduling, personal circumstances, or preference
• Future family building: Using embryos from a previous cycle

Why the Due Date Formula Is the Same

The due date formula depends on the embryo's developmental stage, not its storage history. Here's why:

Vitrification Pauses Development Completely

When an embryo is vitrified (flash-frozen), all cellular activity stops. The embryo doesn't age, develop, or change while frozen. A day 5 blastocyst frozen in 2020 and thawed in 2026 is still developmentally a day 5 embryo—those 6 years of storage time don't count toward its biological age.

Developmental Stage Determines Dating

Pregnancy dating is based on where the embryo is in its developmental journey, not calendar time. Whether an embryo reached day 5 five days ago (fresh) or five years ago (frozen), it's at the same developmental stage at the moment of transfer.

Medical Dating Uses Standard Frameworks

The medical system dates pregnancies using gestational age from a theoretical last menstrual period. For IVF, we back-calculate this theoretical date based on the embryo's developmental stage at transfer. Fresh and frozen embryos of the same age have the same theoretical LMP calculation.

Comparing the Calculations Side by Side

Let's look at two patients with embryos created on the same day but different transfer timings:

Patient A: Fresh Transfer

• Egg retrieval: March 1, 2026
• Embryo developed to day 5: March 6, 2026
• Fresh transfer: March 6, 2026 (day 5 blastocyst)
• Due date: March 6 + 261 days = November 22, 2026

Patient B: Frozen Transfer

• Egg retrieval: March 1, 2026
• Embryo developed to day 5 and frozen: March 6, 2026
• FET transfer: September 15, 2026 (day 5 blastocyst)
• Due date: September 15 + 261 days = June 4, 2027

Both patients use the exact same formula (transfer date + 261 days for day 5). The different due dates simply reflect the different transfer dates—the freezing process doesn't change the calculation.

What Actually Differs Between Fresh and Frozen

While due date calculations are identical, there are real differences between fresh and frozen transfer cycles:

Preparation Protocol

Fresh transfer: No additional preparation needed beyond the stimulation cycle. The body's natural hormones from stimulation prepare the uterine lining.

Frozen transfer: Requires a separate preparation cycle:

• Medicated FET: Estrogen supplements build the lining, followed by progesterone
• Natural cycle FET: Transfer timed to natural ovulation
• Modified natural cycle: Natural cycle with trigger shot and/or hormone support

Time from Retrieval to Transfer

Fresh transfer: 3-6 days after retrieval

Frozen transfer: Minimum one month after retrieval (usually); can be years later

Body Recovery

Fresh transfer: Transfer happens while ovaries are still enlarged and potentially uncomfortable from stimulation

Frozen transfer: Body has fully recovered from stimulation; ovaries back to normal size

Success Rates

Current evidence suggests FET success rates are equivalent to or slightly higher than fresh transfers in many populations. This may be because:

• The uterine environment may be more receptive without stimulation hormones
• Only high-quality embryos survive freezing and thawing
• Better embryo-endometrium synchronization

However, success rates don't affect due date calculations—both fresh and frozen pregnancies develop on the same timeline.

Medication Requirements

Fresh transfer: May require less supplemental progesterone since the body produces it naturally post-ovulation

Frozen transfer: Almost always requires progesterone supplementation until 10-12 weeks (when placenta takes over); medicated FET also requires estrogen

Common Misconceptions

Misconception: Frozen embryos result in a different due date calculation

Reality: The formula is identical. Only the transfer date and embryo age matter.

Misconception: A frozen embryo is "younger" than a fresh one transferred the same day

Reality: Two day 5 embryos transferred on the same day have the same gestational age and due date, regardless of when they were originally created.

Misconception: You need to account for time in the freezer

Reality: Time frozen doesn't factor into any pregnancy calculations. The embryo's biological clock was paused.

Misconception: Using the original retrieval date gives a more accurate due date for FET

Reality: Using the retrieval date would give an incorrect due date. The transfer date is the relevant date for dating purposes.

Special Scenarios

Day 5 Frozen, Day 6 Transfer

Sometimes an embryo frozen on day 5 is thawed and allowed to continue developing before transfer, making it technically day 6 at transfer. In this case, use day 6 calculations (260 days) because the embryo's developmental stage at the actual moment of transfer is what matters.

Embryos from Different Cycles

If you have embryos frozen from multiple retrieval cycles and transfer one from an older cycle, you still use the transfer date for calculations. It doesn't matter which retrieval the embryo came from.

Donor Embryo FET

Even with donor embryos (created from donor eggs/sperm and frozen), the same formula applies. The transfer date and embryo age at transfer determine your due date.

Which Transfer Type is Right for You?

Since due dates are calculated the same way, the choice between fresh and frozen transfers depends on other factors:

Consider Fresh Transfer If:

• You're not at risk for OHSS
• Your lining looks good during stimulation
• You don't need genetic testing
• You prefer fewer cycles/appointments
• Your clinic recommends it for your situation

Consider Frozen Transfer If:

• You're at risk for OHSS
• You want genetic testing (PGT-A/PGT-M)
• Your progesterone rose early during stimulation
• Your lining isn't optimal during stimulation
• Your clinic uses a freeze-all approach
• You need time for other reasons (health, scheduling, emotional readiness)

Discuss with your fertility specialist to determine the best approach for your specific situation.

Using Our Calculator for Fresh and Frozen Transfers

Our IVF Due Date Calculator works identically for both fresh and frozen transfers:

1. Enter your embryo transfer date (the date the embryo was placed in your uterus)
2. Select the embryo age at transfer (day 3, 5, or 6)
3. Choose "Fresh Transfer" or "Frozen (FET)"—this is just for your records and doesn't change the calculation
4. Click Calculate

You'll get your due date, current gestational age, pregnancy progress, and milestone timeline—all calculated the same way regardless of transfer type.

Summary

The key takeaways for fresh vs. frozen transfer due dates:

• Same formula: Both use Transfer Date + Days Based on Embryo Age
• Freezing doesn't count: Time in the freezer isn't added to any calculation
• Only transfer date matters: The date the embryo entered your uterus is what counts
• Embryo age is embryo age: A day 5 blastocyst is a day 5 blastocyst, fresh or frozen
• Real differences exist: The choice affects cycle preparation, timing, and logistics—just not due date math

Whether you've had a fresh transfer or FET, use our IVF Due Date Calculator to determine your estimated due date, track your gestational age, and view your pregnancy milestones.

Frequently Asked Questions

My eggs were retrieved a year ago and I'm doing a FET now. Do I use the retrieval date or transfer date?

Use your transfer date—the date the thawed embryo is placed in your uterus. The retrieval date from a year ago is irrelevant for due date calculation. Your embryo's biological clock was paused during freezing, so it's developmentally the same age it was when frozen, regardless of how much calendar time has passed.

I had a fresh transfer that failed and now I'm doing a FET with embryos from the same retrieval. Will my due date be calculated differently?

The calculation method is exactly the same—you'll just use your new FET transfer date. Each transfer gets its own due date calculation based on that specific transfer date. The failed fresh transfer has no bearing on the FET calculation.

My doctor mentioned my embryo was a "hatching blastocyst" when frozen. Does this change the calculation?

No. Whether your embryo was an early blastocyst, expanded blastocyst, or hatching blastocyst at the time of freezing, it's still considered a day 5 (or day 6) embryo. The expansion stage describes quality and maturity within that day's development but doesn't change the dating formula.

Are there any outcome differences between fresh and frozen transfers that might affect my pregnancy after conception?

Research suggests some differences in pregnancy outcomes, though both approaches result in healthy pregnancies. Some studies indicate FET pregnancies may have slightly higher birth weights and lower rates of preterm birth, possibly because the uterine environment isn't affected by stimulation hormones. However, these differences don't change how due dates are calculated or how pregnancy progresses week by week. Both fresh and frozen pregnancies follow the same developmental timeline.

I'm using frozen embryos from an egg donor. How does that affect my due date?

Donor egg embryos use the same calculation as your own embryos. The due date depends solely on when the embryo was transferred to your uterus and what developmental stage it was at that time. Whether the eggs came from you or a donor doesn't change the formula. If it was a day 5 blastocyst transferred on June 15, your due date is June 15 + 261 days, regardless of the egg source.

Can the type of transfer affect when I should announce my pregnancy?

The type of transfer (fresh vs. frozen) doesn't directly affect announcement timing. What matters is your gestational age, which is calculated the same way for both. Most couples wait until after 12-13 weeks (when miscarriage risk significantly decreases) to announce publicly. Since both transfer types use identical dating, you'll reach this milestone at the same gestational age, just on different calendar dates depending on when your transfer occurred.

The Science Behind Vitrification

Understanding why frozen embryos don't age in storage helps explain why the due date formula is identical for fresh and frozen transfers.

What is Vitrification?

Vitrification is a rapid freezing technique that transforms the embryo into a glass-like state within seconds. Unlike slow freezing methods used in the past, vitrification prevents ice crystal formation, which can damage cells. The process uses cryoprotectants (substances that protect cells from freezing damage) and ultra-rapid cooling to approximately -196°C (-321°F) using liquid nitrogen.

Complete Biological Pause

At these extremely low temperatures, all biological activity ceases completely. Enzymes don't function, cells don't divide, and no metabolic processes occur. The embryo is essentially in suspended animation. Whether stored for one month or ten years, the embryo experiences no passage of biological time.

High Survival Rates

Modern vitrification achieves survival rates exceeding 95% for blastocysts. When properly thawed, embryos resume normal development as if no time had passed. This is why a day 5 embryo frozen in 2018 and transferred in 2026 is still developmentally identical to a fresh day 5 embryo—both are at the exact same stage of development at the moment of transfer.

Historical Perspective: How IVF Transfer Practices Have Evolved

The shift toward frozen transfers represents one of the most significant changes in IVF practice over the past two decades.

Early Days: Fresh Transfers Dominated

In the early years of IVF, fresh transfers were the standard approach. Freezing technology was less advanced, with lower embryo survival rates after thawing. Clinics would transfer multiple fresh embryos to maximize success, often leading to high-order multiple pregnancies.

The Vitrification Revolution

The introduction of vitrification in the 2000s dramatically improved embryo survival rates. This made frozen transfers a viable alternative to fresh transfers, with comparable (and sometimes superior) success rates. Clinics began exploring freeze-all protocols.

Modern Practice: Personalized Approach

Today, the choice between fresh and frozen transfer is individualized based on patient factors, clinic protocols, and specific cycle circumstances. Many clinics now perform more FET cycles than fresh transfers. Despite this shift in practice, the due date calculation has remained consistent throughout this evolution—always based on transfer date and embryo age.

Fresh vs. Frozen Transfer: Key Statistics

Current Fresh vs. Frozen Transfer Split

The vast majority of IVF cycles today use frozen embryo transfers. Here is the current approximate split:

Detailed Protocol Comparison

Understanding the full differences between fresh and frozen protocols helps explain why the due date formula remains the same while the patient experience varies significantly.

Success Rates by Transfer Type and Age Group

Live birth rates vary by age group, but frozen and fresh transfers show comparable outcomes. Data is approximate and based on recent CDC/SART reporting.

Fresh Transfer Live Birth Rates

Frozen Transfer (FET) Live Birth Rates

Note: FET rates may appear higher partly because PGT-A tested (genetically screened) embryos are often transferred frozen, which pre-selects higher-quality embryos.

Advantages and Disadvantages Comparison

Year-by-Year Trend: Fresh vs. Frozen Transfers

The shift toward frozen embryo transfers has been one of the most dramatic changes in IVF practice. This table shows the approximate percentage of transfers that were frozen (FET) vs. fresh over recent years.

Impact on Family Planning

Understanding that fresh and frozen transfers use the same due date calculation can help with family planning decisions.

Timing Your Transfer

If you have frozen embryos and are planning your FET, you can calculate your approximate due date based on potential transfer dates. This might help you plan around work commitments, family events, or seasonal preferences for your due date. Simply add 261 days (for a day 5 embryo) to your anticipated transfer date to estimate when your baby would arrive.

Spacing Pregnancies

If you have additional frozen embryos from the same retrieval cycle and plan future siblings, you can space transfers knowing exactly how to calculate each pregnancy's timeline. Each FET will have its own due date calculated from its own transfer date.

Age of Frozen Embryos

Some patients worry about using embryos that have been frozen for many years. Rest assured that embryo storage duration doesn't affect the due date calculation or pregnancy development. A successfully thawed embryo develops on the same timeline regardless of storage duration. Studies have reported successful pregnancies from embryos frozen for over 20 years.