Intracytoplasmic Morphological Sperm Injection (IMSI) is an additional tool that some clinics use to select the best sperm for injection into the egg. It differs from ICSI only by the way the sperm are chosen for injection. The embryologist uses a very powerful microscope to select sperm which appear to be morphologically normal. Among other things, they are looking for sperm which have normal shaped heads, and the absence of vacuoles which are believed to be related to DNA damage in the cell and reduce the prospect of embryo development.
There have been many research papers describing how IMSI improves embryo development and indeed pregnancy rate but a recent paper published in the reputable journal Human Reproduction appears to add some caution. The new paper found no difference in embryo development following ICSI versus IMSI and suggests that IMSI should not be used on unselected patients. This would make sense as IMSI is an expensive extra in treatment and from the study above seems only useful where there are indications for its use.
Find out which IVF clinics abroad use IMSI as a tool.