In conventional IVF, eggs and many sperm are placed together in a dish and fertilization happens on its own. In ICSI, an embryologist selects one sperm and injects it directly into the egg using a fine glass needle under a high-power microscope. Everything else about the IVF cycle — stimulation, egg retrieval, embryo culture, transfer — stays the same.
When it's used
ICSI is the standard approach when sperm count, movement, or shape is significantly reduced. It is also used when sperm has been surgically taken from the testes, or when a previous IVF cycle showed poor or failed fertilization. For couples without sperm problems, using ICSI routinely doesn't necessarily improve results. It is meant for specific problems, not as an automatic upgrade.