Annotation is the process of identifying exact time-points that represent an event or developmental stage thus assigning is with a value measured in hours post insemination.
For assessment of specific timings (“t”) of embryonic stages, such as “the time at which an embryo reaches the 8 cell stage (“t8”), annotation should take place at the first image frame for which this stage is observed. That is, the first image when there is complete cellular division.
| Morphokinetic event | Definition |
|---|---|
| tPNappearance | Time at which pronuclei formation can be first be identified |
| tPNfaded | Time at which the first image is seen where both pronuclei have faded |
| tn | Time from insemination to completion of division to n cells |
| tSC | Time from insemination to when the first cells of the embryo begin to compact |
| tM | Time from insemination to formation of a morula, where all cells have compacted and cell membranes are unclear |
| tSB | Time from insemination to start of blastulation, when the first sign of a cavity formation between two cells is visible. As the blastocoel cavity grows during blastulation, going back in the image sequence from a definite blastocyst stage may be helpful to obtain this timepoint. |
| tB | Time from insemination to formation of a full blastocyst; when the blastocoele cavity fills the embryo and the frame just before the embryo begins to "pulse" out onto the zona pellucida. |
| tEB |
Blastocyst expansion can occur over several hours and therefore a defined feature is required to pinpoint this timepoint. An expanded blastocyst is the time at which the blastocyst has expanded in diameter to a point where the zona pellucida has reached half of its original thickness, which can be measured and is therefore an objective assessment. |
| THB | Time from insemination to hatching blastocyst, when the trophectoderm herniation through the zona pellucida is first observed |
| Direct cleavage | Direct or rapid (<5hours) cleavage from 1 to 3 or from 2 to 5 cells |
Reference
Ciray, H.N., et al., Proposed guidelines on the nomenclature and annotation of dynamic human embryo monitoring by a time-lapse user group. Hum Reprod, 2014. 29(12): p. 2650-60.