Bottom line up front: The fertility world has shifted toward frozen embryo transfers (FET) as the default approach. Research shows FET produces equal or higher implantation and live birth rates compared to fresh transfers, with lower OHSS risk and better endometrial preparation. Most Colombian clinics now offer freeze-all protocols, though fresh transfers remain appropriate in specific situations.
Why the Shift to Frozen?
During IVF stimulation, high oestrogen levels alter the endometrial lining. The uterus that just endured 10–14 days of hormonal stimulation is not in its most receptive state for implantation. By freezing all embryos and transferring in a subsequent cycle, the endometrium can be prepared under more physiological conditions — resulting in a more receptive lining.
Modern vitrification (ultra-rapid freezing) has made this possible. Embryo survival rates after vitrification exceed 98%, and frozen-thawed embryos perform identically to fresh embryos in clinical outcomes. The old concern that freezing damaged embryos is no longer supported by evidence.
| Factor | Fresh Transfer | Frozen Transfer (FET) |
|---|---|---|
| Implantation rate | 35–45% | 40–55% |
| OHSS risk | Elevated (pregnancy worsens OHSS) | Eliminated (no pregnancy during stim) |
| Endometrial receptivity | Potentially compromised by stimulation | Optimally prepared |
| Time to transfer | 5 days after retrieval | 4–8 weeks after retrieval |
| Allows PGT-A | Tight timeline (results may not return in time) | Yes — results return before transfer |
| Extra cost | None | $800–$1,500 for FET cycle |
| Total trips to Colombia | 1 (retrieval + transfer) | 2 (retrieval trip + transfer trip) or 1 extended |
When Fresh Transfer Still Makes Sense
- Normal responders with moderate egg count (8–15): Lower OHSS risk and endometrial quality is likely adequate
- Patients who cannot easily return for a second trip: Logistical constraints may favour a single-trip fresh approach
- Low embryo numbers: With only 1–2 embryos, transferring fresh avoids the (small) risk of freeze-thaw loss
- Patient preference: Some patients prefer the emotional closure of completing the cycle in one trip
Many international patients do a retrieval trip (5–7 days) followed by a transfer trip (3–5 days) 4–8 weeks later. This allows time for PGT-A results, optimal endometrial preparation, and emotional recovery from stimulation. Colombian clinics are experienced in coordinating this model for international patients.
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