Ultrasound monitoring is the accepted method for monitoring infertility treatment cycles. It allows evaluation of follicle growth, endometrial development, and risk of ovarian hyperstimulation. Transvaginal ultrasound is recommended starting on day 6-8 of stimulation to measure follicle size and number. The leading follicle is typically 18-20mm at the time of hCG trigger. Endometrial thickness should be 7-14mm on the day of trigger. Doppler ultrasound can assess blood flow and predict ovarian response and uterine receptivity. With experienced use of ultrasound alone, additional hormonal monitoring is often unnecessary for cycle monitoring in infertility treatment.