| Morphokinetic event | Definition |
|---|---|
| tPNappearance | Time at which pronuclei formation can be first be identified |
| tPNfaded | Time at which 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 |
| tB | Time from insemination to formation of a full blastocyst; when the blastocoele cavity fills the embryo with less than 10% increase in its diameter |
| tEB | Time from insemination to expanded blastocyst; when the blastocyst has increased in diameter by more than 30% and the zona pellucida has started to thin |
| 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 |
