A fresh transfer places the embryo in the uterus a few days after egg retrieval; a frozen transfer (FET) freezes the embryos first and transfers one in a later cycle. For most patients the success rates are comparable — the real decision is about timing, safety, and when your body is most ready.
The difference is timing, not quality
In a fresh cycle, the embryo is transferred about five days after egg retrieval, in the same cycle in which your ovaries were stimulated. In a frozen cycle, embryos are frozen at the blastocyst stage and transferred in a later cycle — weeks or months on — once the uterus has had time to return to normal.
Freezing is not a downgrade. Modern vitrification (flash-freezing) is so effective that the overwhelming majority of good-quality embryos — typically upwards of 90–95% — survive thawing intact.
Frozen transfers are not "second best" — they let the uterus recover and the transfer be timed well.
Why your doctor may recommend freezing everything
A "freeze-all" cycle, where no fresh transfer happens at all, is now common and usually recommended for specific, good reasons:
- After a strong ovarian response. Stimulation hormones run high in a fresh cycle; transferring into that environment can be less ideal, and in women at risk of ovarian hyperstimulation (OHSS), pregnancy makes OHSS worse. Freezing lets the ovaries settle first — a safety decision.
- When the lining isn't ready. If the endometrium is thin or progesterone rose early, deferring the transfer to a cycle where the lining can be prepared properly improves the odds of that transfer.
- When genetic testing (PGT) is planned. Biopsy results take time, so embryos are frozen while awaiting them.
- For logistics and recovery. A frozen cycle is gentler — no stimulation, fewer injections, more control over timing.
What the evidence says about outcomes
The honest summary of current evidence, without cherry-picking:
- Live birth rates are comparable overall. For most patients, fresh and frozen transfers perform similarly; freeze-all shows a clearer advantage mainly in specific groups (strong responders, OHSS risk, PCOS).
- Frozen transfers are associated with fewer preterm and low-birth-weight deliveries in the research literature.
- Fresh transfers are associated with a lower rate of hypertensive complications of pregnancy, which appear somewhat more often after frozen cycles.
- Storage time doesn't wear embryos out — outcomes from embryos frozen for years remain in the same range as recently frozen ones.
No single option "wins" — which is exactly why the choice should be individual, not ideological.
How the frozen cycle itself works
An FET cycle is much simpler than a stimulation cycle. Either your natural cycle is tracked and the transfer timed to your own ovulation, or the lining is prepared with estrogen followed by progesterone, with a scan to confirm the endometrium is ready. The thawed embryo is then transferred in a short, anaesthesia-free procedure — and the aftercare and two-week wait are identical to a fresh cycle.
How to think about the choice
Ask your doctor these questions rather than searching for a universal answer:
- Is there a medical reason (OHSS risk, lining, PGT) to prefer freezing in my cycle?
- If a fresh transfer is planned, what happens to the remaining embryos? (They're frozen — most IVF cycles end up using both approaches across attempts.)
- What does my clinic's own experience show for someone with my profile?
The good news either way: choosing between fresh and frozen is choosing between two well-proven paths, not between a strong and a weak one.
Frequently asked
Does freezing damage embryos?
With modern vitrification, the large majority of good-quality embryos survive thawing — survival upwards of 90–95% is the norm in well-run labs. Freezing technology is the single biggest reason frozen transfers now perform on par with fresh ones.
Is a frozen transfer more successful than a fresh one?
For specific groups — strong responders, women at OHSS risk, PCOS — freeze-all often performs better. For most others, the two are comparable, and the deciding factors are medical fit and timing rather than a universal ranking.
How long can embryos stay frozen?
Years. Research on embryos stored long-term shows outcomes in the same range as recently frozen embryos — storage duration is not a meaningful factor in success.
Why did my doctor cancel my fresh transfer?
Usually a protective decision: a high response with OHSS risk, a lining that wasn't ready, or early progesterone rise. Deferring to a frozen cycle in those situations is done to raise the chance that the transfer which does happen, works.