Certain patients produce embryos which, although they appear to be viable, are unable to hatch out of the zona pallucida (outer covering) to implant in the uterus. This seems to be especially true of women over 38 years of age. These patients may benefit from assisted hatching, in which the zona is artificially breached by creating a small opening. This is performed after fertilization occurs, but prior to the embryo transfer. Assisted hatching may be employed in patients who have failed to achieve pregnancy despite being able to produce good embryos.