Cati
The Science

Viability Morphokinetic Markers

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Introduction

Viability of the embryo correlates with the embryo’s competence to implant and is expressed by its ability to develop to blastocyst stage in 5-6 days of in-vitro cultivation and to start the process of hatching.

We distinguish between three groups of morphokinetic properties with an impact on viability:

  • Morphokinetics indicating ability to produce relevant number of cells
  • Morphokinetics indicating differentiation of ICM cells into trophectoderm
  • Morphokinetics indicating embryo's ability to Blastocyst Hatching

Morphokinetics Indicating Ability to Produce Relevant Number of Cells

Cleavage Events
definition

The time (t) interval (hrs) between ICSI fertilisation (tCSI) and the occurrence of the cell Cleavage . The cleavage of the cells occur within a specific time frame and is influenced by specific processes of early embryo development.

Tip

The dynamic of the cell shape changes is recognized and expressed by Activity Graph.

note

At present the inherited and meiotic genetic anomalies are not recognisable without preimplantation or prenatal testing. On the other side, the abnormal cleavages (the major source of mitotic aneuploidies responsible for developmental arrest, implantation failure and early miscarriages) can be detected by time‑lapse imaging system.

Number of cells Abbreviation
1 cellt1
2 cellst2
3 cellst3
4 cellst4
5 cellst5
8 cellst8
9 cellst9
17 cellst17
33 cellst33
65 cellst65
129 cellst129
Cleavage Intervals

An interval between the cleavage of the first and the last daughter cells of the same mitotic sequence . This is the duration of the mitotic sequence expressed in hours. The more synchronous cell cleavage is, the more homogeneous developmental competencies of the resulting daughter cells are achieved. Synchronous cell cleavage in a given mitotic sequence is exhibited by a short cleavage interval, and vice-versa.

note

The 3rd mitotic sequences are influenced by embryonic genome activation.

ParameterAbbreviationFormula
2 cells cleavage intervalCI1t2 - tsyng
3-4 cells cleavage intervalCI3-4t4 - t3
5-8 cells cleavage intervalCI5-8t8 - t5
note

CI3-4 and CI5-8cleavage intervals can be monitored with existing time‑lapse systems.

Length of mitotic cycles
definition

Mitotic cycle is a process in which the cells duplicate themselves to create genetically identical copies (daughter cells). The process is accomplished through cell division. The phases of MC are: interphase and mitosis (M-phase).

impact on viability

The more mitotic cycles occur in 5-6 days, the more cells the embryo will have and the better chances for blastocyst expansion/hatching can be achieved.

the list of parameters

Learn more about formulas to calculate lengths of mitotic cycles.

ParameterAbbreviationFormula
Length of 1st mitotic cycleMC1t2 - tICSI
Length of 2nd mitotic cycleMC2t3-t2
Length of 3rd mitotic cycleMC3t5-t3
Length of 4th mitotic cycleMC4t9-t5
Length of 5th mitotic cycleMC5t17-t9
Length of 6th mitotic cycleMC6t33-t17
Length of 7th mitotic cycleMC7t65-t33
Length of 8th mitotic cycleMC8t129-t65
Mitotic Sequences
definition

Mitotic sequences (MSeq) are series of cleavages occurring from the same generation of the cells. The product of each MSeq is a new generation of daughter cells. The more synchronous the timing of MSeq is (expressed as CI), the more uniform developmental competencies of the resulting daughter cells are achieved.

Mitotic SequencesThe result
1st mitotic sequence (1st MSeq)2-cells embryo
2nd mitotic sequence (2st MSeq)4-cells embryo
3rd mitotic sequence (3st MSeq)8-cells embryo
4th mitotic sequence (4st MSeq)16-cells embryo
5th mitotic sequence (5st MSeq)32-cells embryo
6th mitotic sequence (6st MSeq)64-cells embryo
7th mitotic sequence (7st MSeq)128-cells embryo

Morphokinetics Indicating Differentiation of ICM Cells into Trophectoderm

Start of Expansion

Fluid build-up in the blastocoel cavity increases its volume, causing blastocoel expansion and blastocyst growing (i.e. increase of the embryo’s diameter). The blastocoel formation is a proof of TE and ICM differentiation. It is also an essential condition to break Zona Pellucida (ZP) that ultimately has an impact on hatching ability.

Embryonic Cell Compaction

The Compaction is a prerequisite step for cell differentiation.

note

Compaction is not currently detected by CATI.

Morphokinetics Indicating Embryo´s Ability to Hatch

Start of Expansion

The fluid accumulation in blastocoel cavity increases its volume what causes a blastocoel expansion and blastocyst growing (increase of the embryo diameter). The blastocoel formation is a proof of TE and ICM differentiation. It is also an essential condition to break Zona Pellucida (ZP) which has an impact on hatching ability (link).

Blastocoel Collapses

A negative effect on embryo’s ability to hatch. Embryos that exhibit collapse are as likely to hatch as those that do not, but are less likely to implant.

the list of collapses

We distinguish between four types of collapses.

NameDescriptionSegmentation drops by
Big CollapseBig drop of segmentation induced by apoptotic cells elimination — consequence of prior abnormal cleavages>=41%
Medium Mitotic PulseMedium collapses or mitotic pulses caused by physiological cell changes during mitotis21-40%
Small Mitotic PulseSmall collapses or mitotic pulses caused by physiological cell changes during mitotis11-20%
Extra Small Mitotic PulseExtra small collapses or mitotic pulses caused by physiological cell changes during mitotis0-10%
Show on time‑lapse
Blastocyst Hatching

Blastocyst hatching is a natural proces of embryo escaping from its envelope - zona pellucida (ZP) after 5 - 6 days of development. This is a prerequisite step before implantation. In time‑lapse records we see the initial phases of hatching as herniation of trophoectodermic (TE) cells occuring frequently on the place of ICSI needle penetration of ZP.

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