Embryo Freezing & Storage: Complete Guide

If your IVF cycle produces more embryos than you need for immediate transfer, you have the option to freeze (cryopreserve) them for future use. Thanks to advances in freezing technology, frozen embryos now have excellent survival rates and often result in success rates equal to or better than fresh transfers.

Embryo freezing has revolutionized IVF by allowing patients to preserve their embryos for future family building, avoid transferring multiple embryos at once, and separate the stimulation and transfer portions of treatment for medical or logistical reasons.

How Embryo Freezing Works

Modern embryo freezing uses a technique called vitrification—an ultra-rapid freezing process that has largely replaced the older "slow freeze" method used in earlier decades of IVF.

The Vitrification Process

Vitrification works by cooling embryos so quickly that ice crystals don't have time to form. Ice crystal formation was the major problem with older freezing methods, as crystals can damage the delicate cellular structures of embryos. Here's how it works:

1. Cryoprotectant solution: Embryos are placed in a special solution containing cryoprotectants—substances that protect cells from damage during freezing. These solutions replace the water inside cells with protective agents.
2. Flash-freezing: The embryos are rapidly plunged into liquid nitrogen at -196°C (-321°F). The cooling happens so fast (about 15,000-30,000°C per minute) that the solution "vitrifies" or turns into a glass-like solid rather than forming ice crystals.
3. Storage: Frozen embryos are stored in secure cryogenic tanks filled with liquid nitrogen. These tanks have multiple backup systems and alarms to ensure consistent temperature.
4. Thawing: When you're ready to use the embryos, they're warmed rapidly in a reverse of the freezing process. The cryoprotectants are gradually removed and replaced with normal culture medium.

When Are Embryos Frozen?

Embryos can be frozen at different developmental stages:

• Day 3 (cleavage stage): 6-8 cell embryos; less common now but still done in some situations
• Day 5-6 (blastocyst stage): Most common timing; embryos have reached 100+ cells with differentiated structures. Blastocyst freezing is preferred because embryos that reach this stage have demonstrated developmental potential.
• Day 7: Occasionally embryos that are slow to develop can be frozen on day 7 if they reach blastocyst stage

Why Freeze Embryos?

There are many reasons patients choose to freeze embryos:

Medical Reasons

• OHSS prevention: If you're at high risk for ovarian hyperstimulation syndrome, your doctor may recommend freezing all embryos to avoid pregnancy, which can worsen OHSS
• Elevated progesterone: High progesterone during stimulation can affect endometrial receptivity; freezing allows transfer in a better environment
• Polyps or other issues: Uterine issues discovered during monitoring may warrant freezing until they're resolved
• Cancer treatment: Embryos frozen before chemotherapy or radiation preserve fertility options

Genetic Testing

• PGT-A results: Testing embryos for chromosomal abnormalities takes 1-2 weeks; embryos are frozen while awaiting results
• PGT-M results: Testing for specific genetic conditions also requires freezing during the testing period

Strategic/Personal Reasons

• More embryos than needed: If you have multiple good embryos and only want to transfer one, extras are frozen for future siblings or backup
• Better success rates: Some studies show frozen embryo transfers (FET) have equal or better outcomes than fresh transfers, particularly in certain patient populations
• Scheduling flexibility: Separating stimulation from transfer allows more control over timing
• International patients: Traveling home between retrieval and transfer can be more practical

How Long Can Embryos Be Stored?

The short answer: essentially forever. In liquid nitrogen at -196°C, biological processes completely stop. There is no cellular activity, no aging, no deterioration. An embryo frozen for 20 years is biologically identical to one frozen for 2 weeks.

Research on Long-Term Storage

Multiple studies have examined whether storage duration affects outcomes:

• A 2020 study comparing embryos stored for different durations found no difference in survival rates, implantation rates, or pregnancy outcomes between embryos stored for 1 year versus 15+ years
• Studies of children born from long-frozen embryos show no increased rates of birth defects or developmental issues compared to fresh transfers
• The theoretical storage limit is indefinite—as long as proper cryogenic conditions are maintained

Embryo Storage Costs

Storage fees typically include:

• Liquid nitrogen and tank maintenance
• Temperature monitoring and backup systems
• Facility insurance
• Administrative record-keeping

Some clinics offer multi-year packages at discounted rates, which can be cost-effective if you know you'll be storing for several years.

Success Rates with Frozen Embryos

Frozen embryo transfers (FET) have excellent success rates. In fact, some studies suggest they may even exceed fresh transfer success rates in certain situations:

• Survival rate after thaw: 95-99% with vitrification
• Implantation rate: 40-50% per euploid blastocyst
• Clinical pregnancy rate: 50-60% for women under 35
• Live birth rate: 40-50% per transfer for women under 35

The Frozen Embryo Transfer Process

When you're ready to use your frozen embryos, the FET process is simpler than a full IVF cycle:

Natural FET Protocol

• Monitor your natural cycle with ultrasounds and blood tests
• Track ovulation naturally
• Transfer embryo 5 days after ovulation (for day-5 blastocyst)
• May or may not require progesterone support

Medicated FET Protocol

• Take estrogen to build uterine lining (pills, patches, or injections)
• Monitor lining thickness with ultrasounds
• Start progesterone when lining is ready (typically 8mm+)
• Transfer exactly 5 days after starting progesterone
• Continue hormones through first trimester if pregnant

The FET cycle takes about 3-4 weeks from start to transfer, compared to 4-6 weeks for a full IVF cycle with retrieval.

What Happens to Unused Embryos?

Eventually, you'll need to decide what to do with any embryos you don't use. This is a deeply personal decision, and there's no wrong answer. Options include:

Continue Storage

Keep embryos frozen for potential future use. Many people maintain this option for years while deciding.

Donate to Another Family

Embryo donation allows another person or couple to use your embryos to build their family. This is sometimes called "embryo adoption." The process varies by clinic and may involve legal agreements about contact and disclosure.

Donate to Research

Some patients choose to donate embryos to scientific research, which can advance understanding of human development, genetic diseases, and fertility treatments. Research uses are carefully regulated.

Compassionate Transfer

This involves transferring embryos at a time when pregnancy won't occur—such as during menstruation or without hormonal preparation. Some patients find this option more emotionally acceptable than discarding.

Discard

You can choose to have embryos thawed without transfer, allowing them to stop developing. Some patients request a ceremony or ritual around this process.

International Storage Considerations

If you're doing IVF abroad, you have options for where to store your embryos:

Keep Embryos at Original Clinic

• Simplest option—no shipping needed
• Return to the same clinic for future transfers
• Storage costs may be lower in countries like Colombia
• Coordination is straightforward since records are on-site

Ship Embryos to Your Home Country

• More complex logistics and paperwork
• Requires specialized cryogenic shipping containers
• Costs $1,000-$3,000+ for international shipping
• Must coordinate between both clinics
• Some countries have import restrictions or requirements

Most patients find it easier to return for transfers rather than ship embryos, especially when travel costs are factored in and the destination country offers good medical tourism infrastructure.

Embryo Safety and Security

Clinics take extensive measures to protect stored embryos:

• Tank monitoring: 24/7 temperature monitoring with alarms
• Backup systems: Multiple tanks and automatic refill systems
• Chain of custody: Careful identification and tracking protocols
• Dual witness: Two embryologists verify identity at critical steps
• Facility security: Restricted access and surveillance
• Disaster planning: Protocols for emergencies including evacuation

When choosing a clinic, ask about their storage protocols, security measures, and insurance coverage. Reputable clinics are happy to explain their procedures.

Your Embryos, Your Decisions

Throughout the storage process, remember that these are your embryos, and you remain in control of their fate. You can:

• Update disposition forms at any time
• Request transfer of embryos to another facility
• Decide when and whether to use them
• Choose their ultimate disposition

Many people find it helpful to revisit their feelings about stored embryos periodically, as perspectives can change over time. What feels right immediately after IVF may evolve as your family situation changes.

Your embryos are safe, secure, and waiting for you—whenever you're ready. ❄️