In routine IVF, eggs are placed in a laboratory dish in culture media together with prepared sperm. The eggs and sperm are allowed to spontaneously fertilize overnight. The fertilized eggs then develop in the incubator until the embryo transfer procedure, which is usually performed 3 to 5 days after the egg retrieval.

Intracytoplasmic sperm injection (ICSI) differs from IVF in that each egg is individually injected with a single sperm using a tiny needle under microscopic guidance. The resulting embryo is then cultured similarly to an embryo produced in a non-ICSI IVF treatment.

ICSI was initially introduced by the IVF team working at the Brussels Free University in Belgium. At that time, assisted fertilization was being attempted through insertion of the sperm under the eggshell (zona pellucida). The Belgian group took the extra step of injecting the sperm not only under the eggshell but actually into the middle of the egg itself. The first ICSI pregnancies were reported in 1992. Since then, tens of thousands of children have been born as a result of this unique procedure.

Both ICSI and non-ICSI IVF have similar pregnancy rates and outcomes. The embryos produced by either method should not be considered to be superior to those created with the other. ICSI is simply a method to ensure that the egg is fertilized. ICSI is a safe and proven IVF method that does not increase the likelihood that the child conceived in this way will have a birth defect.