Ultrastructural observations in human oocytes and preimplantation embryos after zona opening using an erbium-yttrium-aluminium-garnet (Er:YAG) laser

Abstract

For more than 3 years we have performed laser-assisted hatching prior to embryo transfer in patients with recurrent implantation failure using an erbium-yttrium-aluminium-garnet (Er:YAG) laser system that operates in the infrared region of the light spectrum. The laser beam is guided through a quartz fibre and is brought into direct contact with the zona pellucida. This study was undertaken to evaluate the ultrastructural effects of this laser on the zona pellucida and underlying cell membrane of unfertilized human oocytes and pathologically fertilized preimplantation embryos using light and scanning electron microscopy. The Er:YAG laser produces an almost circular zona opening in the shape of a truncated cone tapering off towards the inside, with a mean diameter of 18 mm. The exact diameter of the drilled site depends on the diameter of the fibre tip and the total number of pulses applied. After laser interaction, the zona matrix and the surface of the underlying ooplasm membrane showed no degenerative alterations. We conclude that the Er:YAG laser is an effective microsurgical tool for achieving reproducible, precise zona openings particularly suitable for purposes of assisted hatching because of their characteristic shape.