IVF/ICSI & the embryology lab
Cleavage vs blastocyst, freeze-all, and luteal support
Last updated: October 2026 — Sources: Cochrane / EAU / ESHRE / WHO / CDC
Key takeaways
IVF success is decided not only in the retrieval room but in the lab: when to transfer, whether to freeze all, and how to support the luteal phase. Decisions here are measured by cumulative live birth, not pregnancy rate per transfer.
Freeze-all in PCOS: live birth 49.3% vs 42.0% and OHSS 1.3% vs 7.1% — but preeclampsia rose (Chen 2016).
Blastocyst: live birth per transfer OR 1.39 (moderate) but cumulative OR 1.24 (low) — Cochrane 2026.
Progesterone supports the luteal phase; hCG raises OHSS — so progesterone is preferred.
Do not judge a lab by pregnancy per transfer — use cumulative live birth.
When to evaluate?
- PCOS or high reserve with OHSS risk — discuss freeze-all before stimulation.
- Few embryos or poor development — the day-3 vs day-5 decision needs a lab discussion.
- Repeated failure despite good embryos — review lab and protocol before adding tests.
What not to do?
- Do not generalise freeze-all to all women — evidence is specific to PCOS.
- Do not force day-5 culture with few embryos — you may lose the transfer chance.
- Do not use hCG as first-line luteal support — it raises OHSS.
Healthcare-professional notice
This hub is independent of NPF products and does not promote them. It is informational only and does not replace individual clinical judgment. Surrogate outcomes (SDF, motility, HOMA, IIEF) are never converted into pregnancy/cure promises, and GRADE certainty is quoted as published.
Binding rule: surrogate outcomes are never converted into patient outcomes. Every certainty grade and limitation is quoted as published.
Deep dive
Freeze-all: for whom?
Greatest beneficiary: PCOS/high reserve with OHSS risk — OHSS prevention is the clearest benefit.
Non-beneficiary: ovulatory woman with normal reserve — results do not support generalisation, and there is a preeclampsia signal.
How to read lab outcomes?
Cumulative live birth includes the fresh transfer and all frozen transfers from the same retrieval — the fair metric.
Pregnancy per transfer can be inflated by selecting better embryos and transferring fewer — it does not reflect programme success.
Evidence in this domain
Each study broken into five questions: why it was run, who was studied, how it was done, the finding, and why it came out that way — then the clinical takeaway and limits, as published.
FAQ
Does freezing harm embryos?
Vitrification now gives high survival, but each extra step carries potential loss — hence freezing without an indication is not justified.
Notice: this reference is informational only and not a substitute for medical advice. Consult your doctor before making any treatment decision.