(ICSI) An in vitro fertilisation technique for overcoming infertility due to oligospermia or azoospermia involving sperm microinjection (SMI), in a sperm is injected through the zona pellucida, across the perivitelline space, through the vitelline membrane (the egg cell's membrane), and directly into the substance (or cytoplasm) of the egg itself. Has completely replaced subzonal sperm insertion (SUZI).