Day 2, Embryo quality
Since we culture all embryos in the embryoscope, we cannot only see how the embryos look the next morning, but also how cell cleavages occurred during the night. This helps us identifying the embryo with the greatest implantation potential.
Two days after oocyte retrieval, the embryos are once more examined in the embryoscope. First at this stage, the embryologist is able to tell something about embryo quality, and the chance of giving rise to a pregnancy.
The optimal embryo has now cleaved into 4 cells of equal size, and there is a visible nucleus in each cell. The embryologist investigates the timing and the synchrony of cell cleavages. In addition, she also looks at the number of small fragments inside the zona pellucida, which represent sequestered cellular material. If there are many fragments, the embryo is not suitable for freezing. The video demonstrates how embryo development looks in the embryoscope..
The zona pellucida
The embryologist also looks at the thickness of the zona pellucida (* on the photo ). In case the zona pellucida is very thick, it may be advantageous to place a small incision in the membrane. This is called assisted hatching (see video link). Before the embryo implants in the uterus, it has to get out of the zona pellucida. This is called hatching. A thick zona pellucida can prevent embryos from hatching. It thus becomes trapped inside the zona pellucida and therefore cannot implant into the uterus.
Good quality embryos
We normally transfer the embryos into the uterus 2 days after oocyte retrieval. If there are several embryos of equal quality, it may be advantageous to culture them to the blastocyst stage, to see what embryo has the greatest chance of pregnancy.