During IVF treatment, a maximum of three  embryos can be transferred to the uterus in any one cycle  treatment. However as ovarian stimulation frequently result in more than 3 eggs being collected during a cycle, extra eggs can be fertilized and the resulting zygotes / embryos can be kept frozen. Patients have the option of having excess embryos frozen for use in subsequent cycles. This freezing process is known as cryo preservation. The benefit of freezing embryos is that they can  be replaced in a future cycle without the patient having to undergo another ovarian stimulation protocol.

	The Single Sperm is picked up by the Micropipette.
	Egg prior to injection. The holding pipette on the left hand side is holding the egg in position, while the smaller injection pipette contains a single sperm.
	The injection pipette is pushed gently into the outer shell of the egg ( Zona pellucida and the inner viteline membrane ) and the sperm is delivered.