O-287 Prognostic value of perivitelline-thread-associated kinetic activity of the plasma membrane of the pronuclear human zygote: a retrospective, observational study
Authors: Browne A , Kourouniadou L , Leitch J 
Published: June 2022

Abstract

Study question
Is perivitelline-thread-associated kinetic activity of the zygote membrane prior to pronuclear fading (tPNf) indicative of the developmental potential of human embryos in vitro?

Summary answer
Embryos displaying kinetic activity of the zygote membrane had a significantly decreased clinical utilization rate, compared to those without.

What is known already
Morphology (pronuclei, cytoplasm etc.) of the pronuclear human zygote has been shown to correlate with ongoing embryo development and implantation potential. Further morphokinetic observations have been noted during this dynamic period of preimplantation development with the use of time-lapse imaging. The hypothesized mechanical actions of perivitelline threads (PVT) have been associated with blastomere fragmentation during early cleavage divisions and subsequent poor embryo development. Their presence and activity prior to tPNf and prognostic value with regard to treatment outcome, have not been studied in detail.

Study design, size, duration
This retrospective study assessed the development of 1047 two pronuclear (2PN) zygotes post IVF/ICSI until culture day 5, from a total of 172 patients which underwent time-lapse imaging monitoring with the EmbryoScope + (Vitrolife) between 01/06/2019 and 20/03/2020.

Participants/materials, setting, methods
Time-lapse videos of embryo development were analyzed manually for the detection and characterization of the ‘event’ of interest: an evident wave of membrane displacement coordinated by PVT prior to tPNf and first cleavage division. Assessed embryos were then categorized into two groups: an event group and a non-event group. The primary outcome of embryo utilization rate was compared between the two groups. Live birth and miscarriage rates per blastocyst transferred were assessed as secondary outcomes.

Main results and the role of chance
Morphokinetic analysis of the event established a mean commencement time at 22.5 ± 9.6 hours, cessation at 27.3 ± 4.7 hours, followed by tPNf at 27.9 ± 5.1 hours post fertilization. A total of 157 embryos in the event group and 890 in the non-event group were assessed (event occurrence rate of 15.0%). The average age of oocyte utilized was not significantly different between the event and non-event group at 34.6 years versus 34.5 years, respectively. The embryo utilization rate in the non-event group was significantly higher than that observed in the event group; 50.6% versus 29.9%, respectively (p &lt; 0.001). The odds of an embryo not being utilized were higher in embryos with an observed event, compared to those without (OR = 2.3; 95% CI = 1.66, 3.45). Live birth rates for fresh blastocyst transfers were 42.9% (6/14) and 29.8% (42/141) for the event and non-event groups, respectively (p &gt; 0.05). Miscarriage rates for fresh blastocyst transfers were 33.3% (3/9) and 35.4% (23/65) for the event and non-event groups, respectively (p &gt; 0.05). Overall, these results indicate that event observation is associated with a significantly decreased embryo utilization rate due to subsequent poor embryo development in extended culture conditions.

Limitations, reasons for caution
A number of events occurring outside the plane of focus prevented accurate assessment, resulting in data exclusion. High levels of variability between the degree of kinetic activity, and transient nature of the PVT were observed. Differences in treatment outcomes were not powered for statistical analysis.

Wider implications of the findings
Notably, embryos displaying kinetic activity of the zygote membrane prior to tPNf are less likely to develop into embryos which can be utilized for transfer or cryopreservation. Observation of the described event may aid with clinical decision-making and managing patient expectations during the period of in vitro monitoring and development.

Trial registration number
Not applicable