Rethinking Fertilisation Assessment in IVF
Are We Discarding Viable Embryos and Transferring Risky Ones?
In most IVF labs, fertilisation is assessed around 16–18 hours after insemination by looking at pronuclei (PN). If two pronuclei are visible (2PN), the zygote is classified as “normal.” Anything else — 0PN, 1PN, or 3PN — is often deemed abnormal and discarded.
But what if that assumption is wrong?
This new study challenges the reliability of morphology-based fertilisation checks and suggests that PGT-A ploidy assessment could both rescue viable embryos and prevent the transfer of genetically abnormal ones.
Study Summary: What We Investigated
Study Question
Can PGT-A ploidy assessment identify viable diploid embryos from non-2PN fertilisation and detect undiagnosed polyploidy in morphologically normal zygotes?
Study Design
- Design: Retrospective
- Sample: 186 embryos (171 2PN, 15 non-2PN)
- Timeframe: January 2023 – January 2024
- Method: All underwent blastocyst biopsy and PGT-A with ploidy evaluation
Key Findings: Why PGT-A Ploidy Assessment Matters
Finding 1: Non-2PN Doesn’t Always Mean Non-viable
- 80% of non-2PN embryos (12 out of 15) were diploid
- Included 6 1PN, 3 3PN, and 3 0PN embryos
- These could have been incorrectly discarded under current protocols
Finding 2: Not All 2PN Embryos Are Safe
- Of 171 2PN embryos, 4 (2.3%) were triploid or haploid
- Without ploidy testing, they would likely have been transferred
These results suggest that relying solely on morphology is not enough. False positives and false negatives in fertilisation classification pose risks — both in missing viable embryos and in transferring abnormal ones.
Why This Changes the Conversation in Embryo Selection
By integrating PGT-A with ploidy assessment into routine clinical workflows, clinics could:
- Recover embryos that would otherwise be discarded
- Avoid transfer of abnormal embryos, improving safety
- Refine embryo selection criteria beyond morphology alone
This approach challenges the conventional embryo classification system and encourages a shift toward molecular validation.
Limitations and Next Steps
Limitations
- Small sample size (n=186)
- Retrospective design
- No outcome tracking post-transfer
Future Work
- Larger, prospective studies needed
- Clinical outcome data following diploid non-2PN transfers
- Broader implementation of ploidy-confirming PGT-A
A Case for Rewriting Fertilisation Assessment
This study highlights the growing need for a more precise, genomically informed approach to embryo evaluation. PGT-A ploidy assessment can act as a powerful safety net — rescuing embryos that deserve a chance, and flagging those that don’t.