Day 6, Hatching
When the blastocyst increases in size, it leads to the zona pellucida becoming thinner and at last there appears a groove in the zona. The blastocyst is now starting to hatch. To begin with, there is only a very small hole. When the pressure rises inside the blastocyst, the hole expands, and finally the whole blastocyst comes out of its membrane. It is now ready to implant in the womb.
Sometimes the zona pellucida hardens so that it does not begin to crack by itself. This is seen especially in elderly women over 40 years and in women who have been treated with very high hormone doses. The zona pellucida can also harden during the freezing process.
In these cases it may be an advantage to perform assisted hatching, where a small sharp needle makes a scratch in the zona pellucida. The scratch does not close again. When the embryo becomes a blastocyst and is about to hatch, it has already paved the way, and the blastocyst comes easily out of the membrane.
Assisted hatching may also be beneficial in women who did not become pregnant in earlier treatments, although the embryos were of good quality.
Many patients ask whether assisted hatching is dangerous and can damage the embryo. In very rare cases it may happen that the embryologist will damage one of the cells when the procedure is done. But it is very rare.