USG monitoring of follicular growth is a number of ultrasound scans carried out by a gynecologist during the period before ovulation (usually every two or three days up until ovulation occurs) in order to check if a woman is ovulating. It involves using ultrasound equipment to check if the egg cells are maturing in the ovaries (how many there are and whether there's one dominant follicle) and measuring the endometrial thickness (whether it is capable of supporting a possible pregnancy). It's the most reliable way to confirm the occurrence of ovulation. Unfortunately USG monitoring needs to happen at the gynecologist’s office and can be costly. Before you decide to monitor your cycle, try to determine ovulation through temperature measurement and body observations. (Is temperature a reliable source to indicate the occurrence of ovulation?)