Understanding Embryo Freezing: Options, Success Rates, and Decisions

Somewhere during the IVF process, you may find yourself facing a question you did not anticipate: what should we do with the extra embryos? It is a question that sits at the intersection of science, finance, ethics, and emotion. And it often arrives when you are already exhausted from the intensity of treatment.

Embryo freezing, or cryopreservation, has transformed modern fertility treatment. What once seemed like science fiction is now routine. Embryos can be frozen, stored for years, thawed, and transferred with overall success rates similar to fresh transfers. This means a single IVF cycle can potentially provide multiple chances at pregnancy.

But it also means decisions. Decisions about how many to freeze, how long to store them, what to do with them if your family is complete, and how to think about embryos that exist in a suspended state of potential. This guide will help you understand the science, the practicalities, and the considerations that come with embryo freezing.

What Embryo Freezing Actually Is

Embryo freezing is the process of preserving embryos at extremely low temperatures for future use. The technique allows embryos created during an IVF cycle to be stored and used later, rather than being transferred immediately or discarded.

The Science of Vitrification

Modern embryo freezing uses a technique called vitrification, which means "turning to glass." Unlike older slow-freezing methods, vitrification cools embryos so rapidly that water molecules do not have time to form ice crystals. Instead, the embryo's contents solidify into a glass-like state.

Why this matters: Ice crystals damage cells. The old slow-freezing methods resulted in more cell damage and lower survival rates; vitrification significantly improves embryo survival. International laboratory standards expect at least 90% of vitrified blastocysts to survive warming, with the best laboratories reaching 99%.

Storage: Vitrified embryos are stored in liquid nitrogen at minus 196 degrees Celsius. At this temperature, biological activity effectively stops. There's no known biological expiry date, although there isn't enough evidence yet to say for certain whether very long storage affects viability. How long you can store embryos is set by law, which differs between countries (see the UAE rules below).

When Embryos Are Frozen

Embryos can be frozen at different developmental stages:

Day 3 embryos (cleavage stage): Contain about 6-8 cells. Historically common, but less so now.

Day 5-6 embryos (blastocysts): Have developed further into a hollow ball of cells with distinct structures. Most clinics now prefer freezing at this stage because blastocysts that have reached this stage have shown good developmental potential and survive vitrification well.

Why Freeze Embryos?

There are several situations where embryo freezing makes sense.

Extra Embryos From an IVF Cycle

A single IVF stimulation often produces multiple viable embryos. If you have more embryos than will be transferred in the fresh cycle, freezing the extras preserves them for:

• Another transfer if the first does not succeed
• A future sibling attempt
• A backup if something goes wrong

The benefit: You avoid going through another full IVF stimulation (with its cost, medications, and egg retrieval) if you need another transfer.

Medical Reasons to Delay Transfer

Sometimes it is better to freeze all embryos rather than doing a fresh transfer:

Ovarian hyperstimulation syndrome (OHSS) risk: When ovaries over-respond to stimulation, a pregnancy in the same cycle can make OHSS worse and longer-lasting. A freeze-all approach lowers the risk of OHSS and allows your body to recover before transfer.

Elevated progesterone: If progesterone rises prematurely during stimulation, the uterine lining may not be optimally receptive, so some clinics prefer to freeze embryos and transfer in a later cycle.

Uterine factors: Polyps, fibroids, or thin lining discovered during stimulation may be better addressed before transfer.

Genetic testing: If embryos are being tested (PGT), results take time. Embryos are frozen while awaiting results, and only those passing testing are transferred later.

Fertility Preservation

For people facing medical treatment that may affect fertility (cancer treatment, for example), freezing embryos before treatment preserves family-building options.

To see how embryo freezing fits within the broader landscape of fertility treatment, visit our Treatments guide.

Frozen vs Fresh Transfer: What the Evidence Shows

For years, the assumption was that fresh embryos had better success rates than frozen. Modern evidence has challenged this assumption.

What Studies Show

A 2021 Cochrane review of randomised trials, including more than 4,700 women, found:

• The overall chance of a baby from an egg collection is probably about the same with a freeze-all approach as with a fresh transfer (around 58% versus 57-63% in the trials)
• Freeze-all lowers the risk of OHSS (from about 3% to about 1%)
• Time to pregnancy is longer with freeze-all, because transfer is delayed
• Freeze-all may increase the risk of high blood pressure disorders in pregnancy and of a larger-than-average baby

When Frozen Can Make Sense

Uterine environment: After ovarian stimulation, the uterus is exposed to very high hormone levels that may affect receptivity. A frozen transfer happens in a more natural hormonal environment.

Lower OHSS risk: This is the clearest proven benefit, especially for women who respond strongly to stimulation.

Time for genetic testing: If PGT is planned, embryos need to be frozen while results come back.

When Fresh Is Preferred

Some doctors still prefer fresh transfers in certain situations:

• When only one or two embryos are available
• When there are no concerns about OHSS or progesterone
• When avoiding the logistics and cost of a separate FET cycle is preferred

The decision between fresh and frozen transfer should be individualised based on your specific cycle and circumstances.

The Frozen Embryo Transfer Process

A frozen embryo transfer cycle is simpler than a fresh IVF cycle because there is no stimulation or egg retrieval.

Protocol Options

Natural cycle FET: Your doctor monitors your natural menstrual cycle, identifies ovulation, and times the transfer accordingly. No medications required (or minimal support). Best for women with regular cycles.

Medicated cycle FET: Estrogen is given (pills, patches, or injections) to build the uterine lining, followed by progesterone to prepare for transfer. Timing is flexible since ovulation is suppressed.

Modified natural cycle: Natural cycle with a trigger shot to precisely time ovulation.

The Timeline

A typical medicated FET cycle:

• Day 1-14: Estrogen to build lining, with monitoring ultrasounds
• Around day 14: Begin progesterone
• Day 19-20: Embryo transfer (5-6 days after starting progesterone for a blastocyst)
• 10-14 days later: Pregnancy test

The Transfer Procedure

The actual transfer is identical to a fresh embryo transfer:

• No anaesthesia required
• A thin catheter is passed through the cervix
• The embryo is deposited in the uterus
• Takes about 5-10 minutes
• Mild cramping is possible but usually minimal

What Happens to the Embryo

Thawing: On the morning of transfer, the embryo is thawed. This takes only minutes. The embryologist assesses whether the embryo survived (95-99% do).

Assisted hatching: Some clinics make a small opening in the embryo's outer shell (zona pellucida) to help it "hatch" and implant. It hasn't been shown to improve pregnancy rates, and NICE advises against offering it.

Success Rates With Frozen Embryos

Success rates for frozen embryo transfer depend on embryo quality, maternal age at the time of freezing, and uterine factors.

General Success Rates

US national data (SART, 2023) show the live birth rate per thaw for frozen transfers that followed a recent egg collection:

These rates are per transfer, so they look higher than per-egg-collection rates: women who have embryos to freeze tend to have a better outlook.

Key point: Embryo quality is largely set by the age when the embryos were created, which is why guidelines judge the outlook for a frozen transfer on the woman's age when the embryos were frozen. Your age at transfer can still matter for pregnancy health.

Factors Affecting FET Success

Embryo quality: Higher-grade blastocysts have better success rates.

Genetics: If embryos were tested (PGT-A) and reported chromosomally normal, the live birth rate per transfer is usually above 50%, even at older ages, although testing doesn't increase the overall number of babies from an egg collection.

Uterine receptivity: Conditions like thin lining, polyps, or adenomyosis can affect implantation.

Protocol: For women with regular cycles, NICE says live birth rates are similar with natural and medicated (hormone-prepared) cycles.

Practical Considerations

Costs

Storage fees: Published annual storage fees are around AED 1,500 to 2,625. Dubai Fertility Center charges AED 1,500 to freeze embryos, including the first six months, and Fakih IVF lists AED 2,625 a year. Fees add up over the years.

FET cycle costs: A frozen embryo transfer costs much less than a full IVF cycle. Dubai Fertility Center lists AED 11,000, excluding medication (2022 price list). Private clinics usually quote on request. See our IVF cost guide.

How Long Can Embryos Be Stored?

There's no known biological expiry date for vitrified embryos. A baby was born in 2025 from an embryo that had been frozen for more than 30 years.

In practice, storage periods are set by law and by your clinic's policies. See the UAE rules below and confirm the details with your clinic.

Transport and Storage

If you move or want to transfer embryos to a different clinic:

• Embryos can be transported between clinics (even internationally) in specialised containers
• This requires coordination, paperwork, and fees
• Not all clinics accept embryos from other facilities

The Emotional and Ethical Dimensions

Embryo freezing raises questions that go beyond the medical and practical.

What Are These Embryos?

Different people view embryos differently:

• Some see them as potential lives with moral status
• Others view them as cellular material with potential but without personhood
• Religious and cultural backgrounds influence these perspectives

There is no universally "correct" answer. What matters is that you and your partner (if applicable) discuss your views and make decisions aligned with your values.

Decisions About Unused Embryos

If you complete your family with embryos remaining, options typically include:

Continued storage: Keep paying storage fees indefinitely. This defers the decision but does not resolve it.

Donation to another couple: Some couples donate embryos to others struggling with infertility. This is not permitted in the UAE under current regulations, but may be an option if you relocate or store embryos elsewhere.

Donation to research: In some jurisdictions, embryos can be donated for scientific research. Not available in all locations.

Disposal: Allowing embryos to thaw without transfer. For some, this is acceptable; for others, it conflicts with their values.

Compassionate transfer: Transferring embryos at a time when pregnancy is unlikely (during menstruation, for example) as an alternative to disposal. Some find this more acceptable emotionally.

Making Decisions as a Couple

Discuss these questions before starting IVF if possible:

• How do we feel about freezing embryos?
• How many embryos are we comfortable creating?
• What would we do with unused embryos?
• What happens if we separate?

Many clinics require couples to sign agreements specifying what happens to embryos in various scenarios (divorce, death of one partner, etc.). These are not just formalities; they are important protections.

Embryo Freezing in the UAE

Regulatory Considerations

UAE law (Federal Law No. 7 of 2019, amended by Federal Decree-Law No. 17 of 2023) sets out who can create and freeze embryos:

• Embryos must be created from the couple's own eggs and sperm; donor eggs, sperm and embryos are not permitted
• Married couples qualify, and so do unmarried couples who are both non-Muslim and have an approved declaration of parentage; Muslim couples must be married
• Both partners must consent to freezing and storage
• Embryos can be stored for five years, renewable on written request. They must be destroyed if either spouse dies, if the marriage ends, if both partners request it, or if storage expires without renewal

See our guide to UAE fertility law for details.

What Happens If You Leave the UAE?

If you relocate, you have options:

• Continue storing embryos in the UAE and return for transfers
• Arrange transport to a clinic in your new location
• Some couples maintain storage in the UAE as a backup

Discuss these possibilities with your clinic before they become urgent.

Key Takeaways

• Embryo freezing uses vitrification, with at least 90% of blastocysts expected to survive warming in a good laboratory.

• Frozen transfers are about as successful overall as fresh, and are preferred in some situations (OHSS risk, genetic testing, suboptimal uterine conditions).

• Age at freezing matters most. Embryos keep the quality they had when frozen.

• Storage costs accumulate over time. Plan for ongoing fees and eventual decisions about unused embryos.

• Ethical and emotional questions about embryo status and disposition deserve thoughtful consideration before and during treatment.

Sources

• Zaat et al. Fresh versus frozen embryo transfers in assisted reproduction. Cochrane 2021 (checked October 2026)
• Rienzi et al. Oocyte, embryo and blastocyst cryopreservation in ART: slow-freezing versus vitrification. Hum Reprod Update 2017 (checked October 2026)
• ESHRE/Alpha: The Vienna consensus on ART laboratory performance indicators (2017, PDF) (checked October 2026)
• SART: National summary report, 2023 (checked October 2026)
• NICE NG257: Fertility problems: assessment and treatment (March 2026) (checked October 2026)
• ASRM: The use of preimplantation genetic testing for aneuploidy (2024) (checked October 2026)
• ASRM: Guidance on the limits to the number of embryos to transfer (2021) (checked October 2026)
• ASRM: Prevention of moderate and severe ovarian hyperstimulation syndrome (2024) (checked October 2026)
• HFEA: Egg freezing (storage and long-term freezing) (checked October 2026)
• Guinness World Records: Baby born from embryo frozen in 1994 (August 2025) (checked October 2026)

This content is for educational purposes only and should not replace professional medical advice. Decisions about embryo freezing involve personal, ethical, and medical considerations. Discuss your specific situation with your fertility team.