You froze your eggs — now what? The decision to use frozen eggs is a different clinical moment from the decision to freeze them. Many women who freeze eggs in their thirties use them several years later; others find they conceived naturally and never need them. This guide focuses on the cycle of actually using frozen eggs: what happens, what the data shows, and what affects your chances.

How a Frozen Egg Cycle Works

Using frozen eggs involves two stages:

Stage 1: Thaw and fertilisation. The frozen eggs are removed from storage and warmed (thawed) in the laboratory. Modern vitrification has survival rates of approximately 80–90% for mature eggs — so if you have 10 frozen eggs, expect approximately 8–9 to survive the thaw. The surviving eggs are then fertilised using ICSI (intracytoplasmic sperm injection — a single sperm injected directly into each egg). This is always done by ICSI rather than standard IVF, as the zona pellucida (egg shell) is slightly hardened after vitrification.

Stage 2: Embryo culture and transfer. Fertilised eggs (embryos) are cultured for 5–6 days to the blastocyst stage. Not all fertilised eggs reach blastocyst — typically 40–60% do. The best-quality blastocyst is selected for transfer; extras are re-frozen as embryos if they are of sufficient quality.

The transfer itself is a frozen embryo transfer (FET) — see frozen embryo transfer guide for detail on the endometrial preparation and procedure.

What the HFEA Data Shows

HFEA publishes outcome data for cycles using frozen eggs (patient's own eggs, not donated). The key figures:

Live birth rate per embryo transfer using own frozen eggs:

  • Eggs frozen under age 35: approximately 20–30% per transfer
  • Eggs frozen at 35–37: approximately 15–22% per transfer
  • Eggs frozen at 38–39: approximately 10–15% per transfer
  • Eggs frozen at 40+: approximately 5–10% per transfer

These figures reflect both the quality of the frozen egg (determined by age at freezing) and the efficiency of the vitrification and thaw process.

The Age That Matters: When the Eggs Were Frozen

The single most important factor in frozen egg success rates is the age of the patient when the eggs were frozen — not the age at which they are used.

An egg frozen at 33 has the chromosomal competence of a 33-year-old egg when thawed and used at 40. This is the fundamental advantage of egg freezing as a fertility preservation strategy: it locks in egg quality at the point of freezing.

This means that a woman using eggs frozen at 32 at age 40 has substantially better expected outcomes than she would attempting IVF with fresh own eggs at 40. The expected success rate tracks with the age at freezing, not the age at use.

How Many Eggs Do You Need?

Working backwards from the expected outcomes helps set realistic expectations:

For eggs frozen under 35:

  • Thaw survival: ~85% (10 eggs → ~8.5 surviving)
  • ICSI fertilisation: ~75% of mature surviving eggs (→ ~6.4 fertilised)
  • Blastocyst development: ~50% (→ ~3.2 blastocysts)
  • Live birth per transfer: ~25%

This suggests approximately 3 usable blastocysts from 10 eggs frozen under 35, giving roughly 3 transfer attempts. Cumulative live birth rate across 3 attempts at 25% per transfer: approximately 58%.

For eggs frozen at 37–38:

  • Lower blastocyst development rate and higher aneuploidy rate reduce the expected yield
  • 10 eggs might produce 1–2 usable blastocysts, with lower live birth rate per transfer

These are averages — individual results vary considerably based on egg quality, sperm source, and laboratory performance.

Partner or Donor Sperm?

When using frozen eggs, sperm can come from:

  • Current partner: Semen sample provided on the day of thaw
  • Stored partner sperm: If the partner's sperm was also frozen (e.g., for medical reasons)
  • Donor sperm: For single women, same-sex female couples, or couples where the male partner is not available or has since separated

The source of sperm does not significantly affect thaw or fertilisation rates, but sperm quality matters as in any ICSI cycle — particularly sperm DNA fragmentation. See male factor infertility.

Common Reasons Frozen Egg Cycles Fail

No eggs survive the thaw. Rare (less than 5% of cycles) with good vitrification, but possible particularly with older eggs or if fewer eggs were frozen.

No fertilisation. Even with ICSI, some mature eggs do not fertilise. ICSI fertilisation failure is typically 5–10%.

No blastocysts develop. A cohort of fertilised eggs may not produce any blastocysts — particularly with older eggs where aneuploidy causes early arrest.

Transfer fails to result in implantation. As with any IVF cycle, even good-quality blastocysts do not always implant. Age at freezing is the main predictor of implantation probability.

Using Eggs Frozen at One Clinic at a Different Clinic

Eggs frozen at one clinic can be transported to another in specialist medical cryoshipping containers. This is worth knowing for patients who:

  • Froze eggs at a clinic they no longer wish to use
  • Move to a different city or country
  • Want to use a clinic that offers better support for the use cycle

Transport costs are typically £300–£1,000 each way. The receiving clinic must have appropriate consent documentation from the originating clinic and must store the eggs under HFEA-compliant conditions.

Frequently Asked Questions

Q: My frozen eggs were stored 7 years ago. Are they still viable?

A: Yes. Vitrification preserves egg quality indefinitely — there is no meaningful deterioration of frozen eggs over years or decades of storage. Eggs stored for 10+ years have been successfully used to achieve live births. The age at which the eggs were frozen (not the storage duration) determines quality.

Q: How many eggs should I thaw at once?

A: Clinics typically thaw all eggs (or a defined cohort) in one session, since thawing a subset is rarely recommended — if insufficient eggs are thawed, the remaining ones may not be of the same quality, and repeat thaw cycles add cost. Your embryologist will advise on the optimal number to thaw based on your total stored and your individual profile.

Q: Can I use frozen eggs if I'm now in a same-sex female relationship (I froze them single)?

A: Yes. Eggs you froze as a single person can be used in any future treatment configuration — with donor sperm if you remain single or are in a same-sex female relationship, or with your female partner's eggs if you are the carrier in a reciprocal IVF arrangement. The consent forms at the time of freezing will have specified how the eggs can be used; check with your clinic.

Q: What happens to frozen eggs if I conceive naturally before using them?

A: Nothing happens automatically — eggs remain stored until you actively request their use, disposal, or donation. Annual storage fees continue. If you no longer want the eggs, you can arrange for them to be destroyed, donated to another patient (through the clinic's donor programme), or donated for research. Contact your clinic to update your instructions.

Q: Are success rates from frozen eggs the same as from fresh eggs?

A: Broadly comparable, and possibly slightly lower per egg used — mainly because the freeze-thaw process results in some egg loss (even with very high survival rates). However, because frozen egg cycles allow careful timing of the transfer and are not subject to the OHSS risk of a stimulated cycle, the endometrial environment may be better. Overall, the differences are modest and the primary determinant remains the age at which the eggs were frozen.

This article is for information only and does not constitute medical advice. Success rates quoted are approximations; discuss your specific expected outcomes with your fertility clinic.