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The day 2 or day 3 embryo after fertilization is usually comprised of four or eight cells, respectively, and is surrounded by the so-called zona pellucida. This is a kind of a coat that protects the embryo during the first days of development. On day 6 of development the zona pellucida breaks, so that the embryo can “hatch” through it and implant in the uterine wall.
In some cases, and due to different causes (e.g., hardening of the zona pellucida, advanced maternal age, etc.), the hatching does not occur. In order to overcome this problem, we can apply a technique known as “assisted hatching”, that consists in making a small hole in the zona pellucida before the transfer, to facilitate the hatching of day 6 embryo after fertilization, leading to higher implantantation and pregnancy rates.
