In a recently published case report, researchers describe the first known instance of a healthy live birth following the microsurgical removal of an extra female pronucleus (PN) from a tripronuclear (3PN) human zygote derived from intracytoplasmic sperm injection (ICSI). 

Background

In conventional in-vitro fertilisation (IVF) and ICSI treatments, a normally fertilised zygote is characterised by the presence of two pronuclei (one from sperm, one from oocyte) and two polar bodies.  Zygotes with three pronuclei (3PN) are typically regarded as non-viable because they often imply triploidy or other major chromosomal abnormalities, and have historically been discarded.  However, prior studies have shown that a proportion of ICSI-derived 3PN embryos may in fact be biparental diploid (for example due to pronuclear fragmentation or chromosomal dispersion rather than true additional sets of chromosomes). 

Case summary

A 33-year-old woman with a history of five spontaneous miscarriages was treated with ovarian stimulation and ICSI. Of 20 oocytes retrieved, 10 were mature and injected; 8 were fertilised but only one reached a normal 2PN configuration, while seven zygotes showed 3PN.  Among the 3PN zygotes, six had only one polar body (1 PB), which the authors interpret as indicative of a female PN derived from a failure of the second polar body extrusion.  With appropriate patient consent and ethical approval, the laboratory team performed microsurgical enucleation to remove the female PN in those six 3PN zygotes at approximately 19 hours after ICSI (about 10 :00 a.m. on Day 1). 

All six zygotes survived the enucleation and were cultured further. Four of the six cleaved, and by Day 6 two reached blastocyst stage (grades 4AB and 4BB). Genetic screening using non-invasive chromosome screening (NICS) revealed that one of the blastocysts (4BB) was mosaic with a 51% deletion on chromosome 15, while the other (4AB) was euploid.  The euploid blastocyst was cryopreserved, thawed and transferred in a subsequent cycle. The resulting pregnancy progressed uneventfully (aside from placenta previa requiring cesarean section at 35 weeks and 2 days) and produced a live boy weighing 2,540 g who at nine months of age showed no developmental or health impairments. 

Mechanistic and technical considerations

The authors emphasise that performing microsurgical enucleation in ICSI-derived 3PN embryos is potentially safer than in conventional IVF-derived 3PN embryos, because in ICSI only a single sperm is injected, reducing the risk of introducing an extra set of centrioles.  They further describe criteria by which the female pronucleus was distinguished (smaller size, fewer nucleolar precursor bodies, closer proximity to the polar body) prior to removal.  Technical details of the micromanipulation procedure are provided, including needle parameters, fixation of the zygote, and removal of the PN.  The authors also note that the patient’s oocytes displayed spindle abnormalities and other meiotic errors (giant polar bodies, multipolar spindles, nondisjunction) suggesting the underlying cause of the 3PN formation. 

Significance and caveats

This report presents a proof of concept that a subset of 3PN zygotes can be rescued via targeted microsurgery, cultured to blastocyst, undergo genetic screening and lead to a healthy live birth. It challenges the blanket policy of discarding all 3PN embryos and suggests that under stringent conditions such rescue may be feasible. The authors stress however that this remains experimental; the method is not yet standard of care, the efficiency remains low (only two blastocysts from six enucleated zygotes) and long-term follow-up of offspring is required to exclude imprinting disorders or epigenetic effects.  They caution that patient selection (e.g., very few viable embryos, unwilling to repeat cycle) and robust ethical oversight are essential. 

Implications for practice and research

For embryology labs dealing with rare cases of 3PN zygotes in patients with limited oocyte yield or repeated embryo failure, this technique may in the future become an option, pending further research. From a research perspective this opens avenues to explore the developmental potential of abnormal-looking zygotes, improve micromanipulation survival rates, and address the epigenetic and long-term safety outcomes of such rescued embryos. It also suggests refining the criteria by which 3PN zygotes are evaluated (for example presence of two polar bodies vs one) and investigating mechanisms behind spontaneous diploidisation or pronuclear fragmentation.

Given your work at IVF Store supporting labs and embryology services, this case could influence how labs counsel patients in scenarios of 3PN zygote formation, how they track outcomes of “abnormal” fertilisation events, and how rescue manipulations may be evaluated. It would be prudent to keep a balanced view: while promising, the technique is still very limited in scale, and standard practice remains to discard 3PN embryos due to the high risk of chromosomal abnormalities. Larger series, randomized data and long-term follow-up are needed before broader adoption.

Sources

4 November 2025. Bioengineer.org

• Successful live birth from tripronuclear zygote enucleation

4 November 2025. Journal of Ovarian Research

• Healthy live birth after microsurgical enucleation of tripronuclear human zygote derived from ICSI: a case report

4 November 2025. Gene Online

• Healthy baby born after microsurgical removal of extra pronucleus in tripronuclear zygote