The human egg is very small and grows within a tiny cyst called a follicle. Each month at the beginning of your cycle, one follicle matures from 5mm, to 20mm on the 13th or 14th day of the cycle, when it ruptures and releases the egg.

It is also possible to release the egg 36-40 hours later by means of an injection (HCG).

Follicle tracking allows us to follow the growth of the follicle by ultrasound. It is carried out to gauge when egg extraction is best performed, and is also performed in conjunction with artificial insemination.