P–223 The necrotic oocyte: does the uncontrolled release of cell contents affect adjacently, group cultured embryos?
Authors: Newman H , Smale H , Barrie A , Campbell A 
Published: August 2021

Abstract

Study question
Is embryo utilisation rate, embryo morphokinetics and the incidence of irregular divisions affected when embryos are group-cultured adjacent to a necrotic oocyte?

Summary answer
This study demonstrates that embryos cultured adjacent to necrotic oocytes appear to be unaffected both in terms of utilisation, morphokinetics and incidence of irregular divisions.

What is known already
Necrosis is a form of uncontrolled cell death, usually resulting from external injury, causing the cell’s contents to release into the surrounding environment1. A cell undergoing necrosis will first visibly swell before the collapse of the plasma membrane causes it to subsequently shrink and the cell to lyse2. An escalation of inflammation occurs due to the release of intracellular factors3. Neighbouring embryos are believed to be negatively affected by a necrotic oocyte with some laboratories choosing to remove necrotic oocytes from culture dishes, however, little is known regarding this impact.

Study design, size, duration
The project was a single site, retrospective cohort analysis using time-lapse data from August 2017 to December 2018. Only patients with at least one necrotic oocyte, a minimum of one adjacent embryo to the necrotic oocyte and those cultured in the EmbryoScope+® were included in the analysis.

Participants/materials, setting, methods
The study included 868 embryos from 89 patients. The embryos were categorised as adjacent to a necrotic oocyte (group 1, n = 208) and not adjacent to a necrotic oocyte (group 2, n = 660). The utilisation rate and irregular division rate were analysed using a Chi-squared test, the morphokinetic parameters was analysed using a t-test. Morphokinetic data included; tPB2, tPNa, tPNf, t2, t3, t4, t5, t6, t7, t8, t9, tSC, tM, tSB and tB.

Main results and the role of chance
Utilisation rate between the two groups was not significantly different (group 1; 40.9% versus group 2; 47.6%, p = 0.09). Incidence of irregular division was not significantly different between the two groups (group 1; 24.0% vs group 2; 21.7%, p = 0.51). No morphokinetic parameter was statistically significantly different when comparing group 1 to group 2, respectively: tPB2, 3.61 vs 3.73, p = 0.38; tPNa, 7.01 vs 6.91, p = 0.59; tPNf, 23.64 vs 23.66, p = 0.95; t2, 3.44 vs 2.98, p = 0.09; t3, 14.56 vs 14.41, p = 0.75; t4, 15.96 vs 15.8, p = 0.77; t5, 15.96 vs 15.8, p = 0.77; t6, 30.33 vs 30.46, p = 0.86; t7, 33.11 vs 33.16, p = 0.95; t8, 37.93 vs 36.92, p = 0.34; t9, 48.66 vs 48.97, p = 0.73; tSC, 58.04 vs 57.89, p = 0.88; tM, 74.02 vs 73.76, p = 0.8; tSB, 75.55 vs 75.42, p = 0.9; tB, 87.06 vs 87.2, p = 0.91.

Limitations, reasons for caution
The time at which the oocytes became necrotic was not analysed therefore the effect, if any, of exposure time could not be determined. Of the 169 necrotic oocytes, two were from IVF and 167 from ICSI; the increased exposure of the embryos derived from ICSI was not controlled for.
Wider implications of the findings: Necrotic oocytes are easily identified in standard culture observations and in time-lapse imaging, therefore, their removal may be an unnecessary practice. More harm could be caused by removing the dish from the incubator, as this would unnecessarily expose any viable embryos contained within the dish to a suboptimal environment.

Trial registration number
Not applicable