After follicular puncture, we prepare the retrieved eggs for artificial fertilisation. The procedure differs depending on the quality of the semen: either traditional in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI).
For IVF, some 100,000 motile sperm cells are added to the mature egg cells in a petri dish or test tube.
This is why it is called in vitro - in glass. Fertilisation takes place by means of a sperm independently penetrating an egg cell. To support optimal development of the combined sperm and egg, they are stored in an incubator that mimics the conditions of the fallopian tube. Each couple is allocated a separate compartment. This means there is no risk of mix-ups.
After around 20 hours, the fertilised eggs are in the pronuclear stage. In this phase, the egg cells to be developed into embryos are selected.
Excess fertilised egg cells can be frozen in liquid nitrogen (cryopreservation) and then stored for later treatments. Later treatment cycles with these cryopreserved egg cells in the pronuclear stage are called freeze-thaw cycles.