When sperm is extracted directly from the testicle by a procedure called testicular sperm extraction (TESE) ICSI is always used. ICSI is also occasionally used in situations where there are a very low number of eggs to fertilize.he dish is housed in an incubator overnight to keep the egg and sperm at room temperature. They are left along for 16 to 20 hours at which point the embryologist can check the eggs to see if the sperm was able to fertilize the egg normally. ICSI (intracytoplasmic sperm injection).