OPINION- Assisted hatching: routine or selective application in IVF

The implantation rate of apparently normal embryos in IVF/ICSI programs has been reported to be 10% to 15% for day 2 or day 3 transfers and 23% to 25% for blastocyst transfers. The hatching process of blastocysts is still not completely understood. In vitro culture of mammalian embryos alters the architecture of their zona pellucida; in vitro derived embryos have thicker zonas, especially the inner layer of zona pellucida. A high proportion of morphologically normal blastocysts have hatching difficulties, and 54% fail to hatch after 8 days of in vitro culture.Assisted hatching was developed as a remedy for this type of implantation failure. Several techniques for assisted hatching have been introduced over the years including; drilling a hole in the zona pellucida, three dimensional partial zona dissection, thinning the zona pellucida, or total removal of the zona. These techniques can be performed chemically, mechanically, by using a LASER beam or a piezoelectric method. Although routine performance of assisted hatching on all embryos in IVF/ICSI patients is neither scientific nor appropriate, there is convincing evidence in the literature that assisted hatching increases the implantation capability of some of the embryos. The proposed indications for assisted hatching are advanced maternal age (≥37 years), elevated basal FSH of women, 2 or more previously failed IVF attempts, embryos with thick zona pellucida (>15 μm), abnormal or poor embryo morphology and retarded developmental rate of the embryo.

Keywords
Assisted hatching, Zona pellucida, implantation, LASER, Zona drilling, Tyrode's solution