In natural gestation, the oocyte (egg) is fertilized by the sperm in the fallopian tube, and the resulting embryo develops for five days before being transferred to the uterine cavity, reaching the endometrium at the blastocyst stage.

Inside the uterus, the embryo hatches through the outer layer, called the zona pellucida. This hatching is essential for embryonic implantation. The zona pellucida is an important layer in natural pregnancy and  classic IVF  to prevent the penetration and fertilization of more than one sperm.

It is the structure that surrounds the oocyte, also the pre-embryo, during the early stages of its development and remains intact during the first cell divisions until the blastocyst stage. At this stage, the internal pressure exerted by the growing embryo forces the thinning and subsequent rupture of the zona pellucida for implantation of the embryo.

Laser-assisted hatching: a technique to facilitate embryo implantation.

 Laser-assisted hatching (a form of energy fired with extreme precision onto the zona pellucida, creating an opening), currently more common and with better results, is a technique performed in embryology laboratories that helps in the  process of opening the zona pellucida  (the glycoprotein layer surrounding embryos) to facilitate the hatching of the embryo inside the uterus on the day of transfer.

It is usually indicated for couples who are already trying in vitro fertilization without success in embryo implantation in the uterus (endometrium). One of the reasons that can explain implantation failure is the fact that many embryos are unable to leave the zona pellucida. It can also be performed when embryologists notice that the embryo's zona pellucida is too thick.

Recommendations for the Assisted Hatching technique

 According to the American Society for Reproductive Medicine (ASRM), the technique increases implantation and pregnancy rates for women with:

• Zona pellucida with increased thickness, typically observed in  women over 38 years of age  with high FSH concentrations;

• Embryos of poor morphological quality;

• Repeated implantation failures in other assisted reproduction attempts;

• Transfer of frozen and thawed pre-embryos.

This procedure is not suitable for all cases and should be discussed with a specialist physician.