Assisted hatching (AH) is the use of physical or chemical methods to artificially open a window or door in the zona pellucida, the “eggshell” or “chrysalis” of the embryo, to facilitate the “emergence” of the embryo from the zona pellucida. This facilitates the embryo’s emergence from the zona pellucida, just like the “cocoon into a butterfly”, and promotes the implantation of the embryo into the endometrium, thus increasing the chances of pregnancy. The zona pellucida is a protein structure wrapped around the egg sister and outside the baby embryo, and is round and spherical. Whether in vivo or in vitro, after fertilization, the embryonic baby needs to go through a developmental process of about 5-6 days to grow into a blastocyst, and this process is carried out in this safe and comfortable “eggshell”, so this “eggshell” is also called the early embryo The baby’s sweet little coat. The outer layer is thicker but easy for sperm to penetrate, while the inner layer is thinner and not easy for sperm to penetrate. “The eggshell acts as a physical barrier to protect the egg sister and the baby embryo from foreign pests; during fertilization the eggshell assists a single sperm to penetrate through the receptor, while preventing abnormal fertilization caused by multiple sperm entering (this is polygamy); after fertilization, the presence of the zona pellucida ensures that constant cell division takes place. After fertilization, the presence of the zona pellucida ensures the structural integrity of the baby embryo, which is constantly dividing cells. The embryonic baby needs to shed its own coat when it reaches a certain stage of development – hatching: But when the embryonic baby reaches a certain stage of development (blastocyst stage), it is time to metamorphose – to shed its coat and enter the embrace of the mother’s womb. Under normal physiological conditions, when the embryo reaches the blastocyst stage, the zona pellucida is gradually thinned as the blastocyst expands; and at the late blastocyst stage, the zona pellucida is so thin that it can be easily broken through, just like a bulging balloon. Only the embryos that hatch can enter the endometrium to complete the implantation process and continue to develop into a fetus; those that do not hatch have only one way out – to become “woof eggs” in their shells. If, for some reason, the embryo cannot hatch on its own, implantation into the endometrium will be difficult, resulting in implantation failure. Which embryonic babies need assistance with hatching? Usual reference factors include: condition of the zona pellucida (thickness, shape, uniformity), embryo quality, maternal age, FSH level, IVF treatment history, etc. 1. abnormal zona pellucida Too thick: when the baby embryos are too thick (>18 μm), they cannot take them off by themselves and should be assisted to hatch; irregular shape: the irregular shape of the embryos increases the difficulty of hatching the baby embryos (strange clothes are always harder to take off) and can be assisted to hatch; dark color: the zona pellucida becomes unattractive, such as presenting a brownish or dark color, consider assisting to hatch. 2. Frozen eggs and embryos After freezing and thawing, the zona pellucida will harden, just like a frozen cotton jacket in the snow, which is difficult to take off. Therefore, frozen eggs and embryos are one of the regular indications for assisted hatching. 3. Poor quality of embryos The potential of these embryos is poor and their ability to hatch on their own is greatly diminished, so they need to be assisted to hatch. 4. Old maternal age As the maternal age increases, the zona pellucida of her embryos usually becomes thicker and harder and loses its elasticity, causing difficulties in natural hatching of the embryos. It is recommended that if the mother is older than 38 years old, her embryo baby should be given assistance for hatching. 5. Basal FSH level If the basal FSH is too high (>15mIU/ml) on the 3rd day of menstrual cycle, it usually indicates poor functional status of the ovaries, poor follicular development environment with abnormal structure or poor function, assisted hatching will improve the implantation rate of such embryo babies. 6. History of previous failed IVF treatment For patients with a history of failed IVF treatment, assisted hatching is recommended. Common methods of assisted hatching: mechanical, chemical and laser methods. The chemical and mechanical methods were first used in clinical practice; the laser method requires special equipment and is now gradually being used more widely in clinical practice. 1. Mechanical method With the help of a small needle, part of the zona pellucida is pierced and the needle is repeatedly rubbed until the zona pellucida is worn through and a cleft is finally formed on the zona pellucida. The embryo is then rotated 90 degrees and the above operation is repeated, and eventually two crossed clefts are formed on the zona pellucida (the baby embryo can be hatched from this cleft after it develops into a blastocyst). 2.Chemical method Using a small tube, the Acid Tyde’s solution/enzyme solution is aspirated and then spit onto the zona pellucida, where it dissolves to form a small hole with a diameter greater than about 20 microns (the embryo baby can hatch from this small hole once it develops into a blastocyst). 3.Laser method The laser method refers to the use of laser beams to make holes in the zona pellucida, which is very precise and can form clefts and small holes in the zona pellucida or thin the zona pellucida, which can be operated in a variety of ways and greatly increases the effect of assisted hatching. Our center mostly uses the laser method.