O-180 What is the true potential of 1PN embryos? A report on utilisation and live birth rates following PGT-A and biparental testing
Authors: Ussher C , Holden S , Bowman M , McArthur S 
Published: June 2023

Abstract

Study question
What is the developmental potential of monopronuclear (1PN) embryos, and does allowing their use only after confirming biparental inheritance offer a clinical solution for them?

Summary answer
1PN embryos demonstrate clear utilisation, euploidy, and live birth rates, that warrant their routine culture, and use following biparental inheritance testing, in the clinical setting.

What is known already
Embryos only displaying a single pronuclei (1PN) are widely regarded to be abnormal and not suitable for clinical use. It is therefore common practice to discard these embryos following fertilisation check. However, 1PN embryos have shown the ability for normal blastocyst development, albeit at a decreased rate, and the ability to produce live births.
To bridge the gap between discarding an “abnormal” 1PN embryo, and the knowledge that it can result in a live birth, our clinic utilises PGT-A with biparental inheritance testing to assess the fitness of a 1PN embryo for transfer.

Study design, size, duration
A retrospective analysis was performed of 5010 1PN embryos derived from IVF (2612) or ICSI (2398) insemination at Genea clinics across Australia between January 2017 and November 2022.
Blastocyst development, euploidy, parental inheritance, pregnancy, and live birth rates were analysed.

Participants/materials, setting, methods
Embryos were defined as being 1PN by the appearance of one pronuclei at fertilisation check 16-18 hours post insemination. Time lapse footage was reviewed on day 3 of culture to eliminate the late appearance of a second pronucleus. Suitable embryos underwent trophectoderm biopsy for PGT-A and biparental inheritance testing. Only euploid embryos with confirmed biparental inheritance were available to patients for frozen embryo transfer.

Main results and the role of chance
1PN embryos derived from ICSI insemination were found to have a significantly lower blastocyst development potential of 17.4% compared to 33.7% for IVF embryos (p &lt; 0.0001). The utilisation rate was also significantly lower at 8.1% for ICSI vs 21.2% for IVF (p &lt; 0.0001).
The IVF embryos showed a higher rate of euploidy following PGA-T testing, 50.9% for IVF vs 37.9% for ICSI (p &lt; 0.0001).
Uniparental inheritance, an indication the 1PN appearance was caused by parthenogenesis, was only observed in 6.7% of the total embryos tested, with IVF embryos having a considerably lower rate of 1.8% vs 20.5% for ICSI (p &lt; 0.0001).
There was no significant difference between the 2 groups for pregnancy rate or live births, following single embryo transfer, with 58.6% for IVF vs 62.9% for ICSI (p = 0.6) and 39.6% for IVF vs 45.7% for ICSI (p = 0.5) respectively. These levels were comparable to normally fertilised (2PN) euploid embryos across Genea clinics in the same time period. During the study period there have been 175 1PN embryos transferred that has resulted in 69 live births from embryos that otherwise would have been discarded.

Limitations, reasons for caution
The use of timelapse imaging from the time of insemination for ICSI embryos, as opposed to 16-18 hours post insemination for IVF embryos may play a role in the type of 1PN embryos that are being identified in each group.

Wider implications of the findings
This study demonstrates that not all 1PN embryos are abnormal and their routine use in the clinical IVF lab in conjunction with appropriate testing should be re-evaluated.

Trial registration number
not-applicable