In Vitro Development
| The oocyte after ovulation/ oocyte retrieval |  |
Cumulus cells surround the oocyte. One purpose of these cells is to prevent all the spermatozoa from arriving at the surface of the oocyte at the same time |
| The oocyte without its surrounding cells. Visable is the protein coat called the Zona Pellucida surrounds the oocyte |  |
A few cumulus cells remain. |
| 1st day- the fertilized oocyte contains 2 nuclei (one containing half the DNA of the mother, the other half the DNA from the father) |  |
2 pronuclei are visible to the embryologist, 16-20 hours after fertilization |
| 2nd day-The developing embryo at the 4 cell stage. |  |
Visable are four blastomeres (cells). |
| 3rd day- 8-cell stage. |  |
All cells are the same |
| 5th /6th day – The blastocyst stage. The blastocyst increases in volume and hatches from its protein coat |
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The cell start to become specialized-Outer cells that will become the placenta and inner cells (at "6 o' clock") that will become the actual embryo. |
