This growing follicle can be seen by Transvaginal ultrasound daily- This is called follicular study. The study starts around 8th to 10th day of menstrual cycle and continues till the follicle ruptures. It usually ruptures after it achieves 20 mm size.

At what size egg will release?

When your follicles have reached around 18-20mm in diameter they are deemed ready for egg collection. You'll be given a hormone trigger injection to stimulate your follicles to release the mature eggs that have been prepared in your follicles.

What is a good size follicle for fertilization?

Follicles of 16–22 mm are more likely to yield mature oocytes than smaller follicles, while larger follicles would more likely yield “post-mature” oocytes that are not competent for fertilization [6].