Intracytoplasmic sperm injection, also known as ICSI, is a fertility treatment used in certain cases of infertility. In ICSI, a doctor injects a single sperm directly into an egg in a lab. The egg and sperm are then placed in an incubator and left to fertilize and grow. If fertilization occurs, the fertilized egg (embryo) is then transferred to the woman's uterus in hope that it will attach itself and result in a pregnancy. This treatment is often used when a man has low sperm count or if the sperm has difficulty penetrating the egg.