This document discusses monitoring of the ART (assisted reproductive technology) cycle. It describes various methods for monitoring, including ultrasound to measure follicle growth and endometrial thickness, as well as using ultrasound combined with serum estradiol levels. The key objectives of monitoring are outlined, such as predicting ovarian response, monitoring pituitary suppression, evaluating gonadotropin dose, preventing OHSS, determining the optimal time for hCG administration, and avoiding cycle cancellation. Indicators for when to adjust gonadotropin dosage or cancel the cycle are provided. Ultrasound is identified as the most practical monitoring method and combining it with estradiol is particularly useful for high-risk patients.