Many women monitor ovulation by testing their body temperature. The vast majority of foreign scholars believe that basal body temperature (BBT) monitoring of follicles is too cumbersome and imprecise and should be eliminated. It is used abroad only as a reference for anovulation and cannot be used to monitor follicular development, let alone as a self-test for infertility. 1. Ultrasonographic manifestations of follicular development in normal menstrual cycle (1) Time of follicular appearance: multiple follicles develop simultaneously at the beginning of each menstrual cycle, but generally only 1 or 2 follicles develop to maturity, called the main follicle (dominant follicle), and the rest follicles are atretic one after another. Some authors have reported that more than 90% of cycles have only one follicle that grows rapidly to maturity, and 5%-11% have two primary follicles developing. The earliest time of follicular ultrasound visualization can be on day 5-7 of the menstrual cycle, showing a minimum diameter of 4-5 mm. (2) Follicular growth rate: ultrasound reveals small follicles in the ovary on day 3-5 of the menstrual cycle, which grow gradually, with ovulation occurring on the average 14th day of maximum size. The main follicle grows an average of 1.5mm per day from day 5 of menstruation until ovulation; an average of 1.2mm per day until day 10 and an average of 1.9mm 4 days before ovulation until the follicle is developed and mature. (1) The follicles are round or oval in shape, with a diameter of 15-25 mm (21.2+-0.53 mm) and an echogenic area within the follicle, which is clear and pure with clear borders and thin walls. (2) In 20% of mature follicles, the day before ovulation, the image of the cumulus oophorus is seen, with short strong echogenicity in the follicle near the wall. 3. Ultrasound images of follicles near ovulation (1) The presence of the oophorus is about 20%, mostly in >18 mm mature follicles, and predicts that ovulation occurs within 24 hours. (2) The perifollicular transmissive ring, which forms as the lh value rises and the membrane tissue becomes edematous and the granulosa cells separate from the membrane layer cells. Ovulation is predicted to occur within 24 hours. The current ultrasound shows a very low chance. (3) The granular layer cells of the follicular wall are completely separated from the bottom layer of the membrane tissue, and the follicular wall appears to be dentate. 4. Post-ovulatory ultrasound manifestations (1) disappearance of mature follicles, accounting for about 80% of cycles. (2) Follicles are reduced in size, with thick walls, blurred borders and light spots inside. (3) Follicles are porous in shape and disappear within 24 hours. (4) A small amount of fluid is seen in the rectal fossa of the uterus after ovulation in about 40% of cycles, with a thick diameter of about 4-6 mm.