Follicular ultrasound is the use of a vaginal probe or abdominal ultrasound to monitor the development of eggs. This is one of the first steps to take when examining infertility.

Normally, a woman's menstrual cycle is about 28-30 days and there will be one ovulation. The ovulation phase is when the ovarian follicle has grown to a certain size (16-26mm) and then ruptures and is released to a pre-accepted fallopian tube in the uterus.