O-181 Utilisation of monopronucleated (1PN) embryos and potential clinical benefits for patients
Authors: Perry S , Wells D , Batha S , Babariya D , Moore C , Nicopoullos J 
Published: June 2023

Abstract

Study question
Is it beneficial to culture 1PN embryos for clinical use?

Summary answer
Culturing 1PN embryos to blastocyst for potential clinical use is beneficial to all patients, especially those with low prognosis.

What is known already
1PN embryos are those with only a single pronucleus visible at the time of fertilisation check. It is generally assumed that such embryos are haploid, having only 23 chromosomes in each of their cells. Given that haploid embryos are not viable, current guidelines recommend only transfering embryos where two pronuclei are visualised. Embryo biopsy at the blastocyst stage, followed by testing with next-generation sequencing (NGS), combined with analysis of DNA polymorphisms, can reveal whether 1PN embryos are truly haploid, or whether normal fertilsation has occurred. Previous studies have shown that in some cases a diploid chromosome number may be present.

Study design, size, duration
A new clinical policy was put into practice to culture all 1PN embryos to day 5/6. This is an ongoing study initiated in April 2022. The data reported are from an eight month period, up until December 2022. During this time, we cultured 288 1PN embryos from 203 patients. Trophectoderm biopsy specimens were shipped to a specialist genetics laboratory where they underwent PGT-A using a method that assesses chromosome copy number and polymorphisms in tandem.

Participants/materials, setting, methods
If embryos were assessed at fertilisation check and found to be 1PN they were not discarded, but rather they were maintained in culture. If any such embryos successfully produced a blastocyst the patients received counselling from their fertility consultant and an embryologist, giving them the options to either go ahead with transfer (only IVF derived), have the embryos genetic status clarified using PGT-A, freeze without testing, or to discard the embryo.

Main results and the role of chance
Of the 288 1PN embryos cultured (IVF and ICSI derived) 85 displayed signs of blastulation (29.5%). 134 of these were derived from ICSI with 20 forming blastocysts (14.9%). 154 were derived from IVF with 65 forming blastocysts (42.2%). Three IVF derived 1PN embryos have been transferred. Currently one is an ongoing singleton pregnancy, one is an ongoing twin pregnancy and the third has resulted in a live birth. 35 embryos were biopsied and underwent genetic testing to confirm their ploidy status. Six of these were ICSI derived, four of which were found to be haploid and two diploid. The other 29 tested embryos were derived from IVF. Of these, 27 were found to be diploid (93.1%) and two were shown to be triploid (6.9%). None were confirmed as haploid. Traditionally, PGT-A methods using NGS examine relative chromosome copy number, but in cases of haploidy/triploidy all of the chromosomes are decreased/increased in number, meaning there is no change in the relative number of individual chromosomes. We established embryo ploidy status using an advanced PGT method, genotyping thousands of polymorphisms scattered across the genome, which are essential for accurate diagnosis of haploidy/triploidy.

Limitations, reasons for caution
The sample size for genetically tested ICSI derived 1PN’s is currently too small to clearly determine whether culture and testing of these embryos is beneficial to the patient. Patients who decided to transfer an embryo categorised as 1PN were made fully aware of the potential risks in doing so.

Wider implications of the findings
These findings show that the culture of 1PN embryos is clinically beneficial to a large number of patients, especially those with poor prognosis who would otherwise have had a failed cycle. Genetic testing demonstrates that IVF derived 1PN embryos that reach the blastocyst stage are likely to have fertilised normally.

Trial registration number
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