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 (the lining of the uterus) is thin or progesterone rose early, moving the transfer to a later cycle lets the lining be prepared properly. That improves the odds of the 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
What current research shows:
- 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 high blood pressure problems in 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.
Neither option is better for everyone. That's why the choice should be made for you as an individual.
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?
Either way, fresh and frozen transfers are both well-proven options. Neither is the weak choice.
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. What does track success is the age you were when those embryos were frozen — see frozen embryo transfer success rates by age.
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.
Do babies from frozen transfers grow differently from babies from fresh transfers?
Some research has found babies from frozen transfers tend to have a somewhat higher average birth weight than babies from fresh transfers, alongside the lower rate of preterm and low-birth-weight delivery already noted above. This is a population-level pattern from the research literature, not something that predicts any individual baby's growth, and it isn't a reason on its own to prefer one path over the other — the right choice for you is still decided by your clinical picture (ovarian response, lining readiness, OHSS risk, and whether genetic testing is planned), not by this one factor.