What is follicle monitoring? When the follicle reaches a certain stage of development, it protrudes significantly from the surface of the ovary. With the surge of follicular fluid, the internal pressure rises, causing the protruding ovarian tissue to become thinner and thinner, and finally rupture, the secondary oocyte and its peripheral zona pellucida and radiating crown are expelled from the ovary together with the follicular fluid. Look at the picture below, this is how the follicles come out! Why is it that most married women who come to our clinic for their first visit are scheduled for a vaginal ultrasound instead of an abdominal ultrasound? This is mainly because the vaginal ultrasound probe is positioned closer to the uterus, adnexa and pelvic cavity, with clear images, high resolution and more accurate test results. Through this test, the doctor can initially understand the size of the patient’s uterus, the condition of the endometrium, the presence of neoplasia, the size of the ovaries, the number of sinus follicles, the size of the dominant follicle, etc., providing an imaging basis for the patient’s subsequent diagnosis and treatment. Why would I choose vaginal ultrasound for ovulation monitoring? Although there are various methods to monitor ovulation, such as menstrual cycle projection, cervical mucus observation, basal body temperature monitoring, ovulation test strips monitoring, etc., vaginal ultrasound monitoring is by far the most accurate method among all methods to monitor ovulation. It can not only clarify which side of the ovary is ovulating and observe the number and shape of the follicles, but also measure the size of the follicles and the thickness of the endometrium. Time to monitor follicles Ultrasound can distinguish follicles of 2-4 mm, so small follicles can be detected in the ovary by vaginal ultrasound on day 3-5 of the menstrual cycle, after which the follicles grow gradually, with the main follicle growing by an average of 1.5 mm per day (by day 10: 1.2 mm per day, up to 4 days before ovulation: 1.9 mm per day) until the follicle matures and is expelled from the ovary. Generally, starting from day 9 of the menstrual cycle, an ultrasound examination is done once every 2 days, and continuous observation will show the gradual growth and migration of the follicles; around day 9-12, the dominant follicle is identified; when the follicles are found to be 16 mm in diameter, monitoring should be changed to once a day; around day 14, the maximum follicles can reach 17-22 mm; when the largest follicles disappear, it indicates that ovulation may occur. Warm tip: Since ovulation monitoring is a continuous monitoring process, if you can choose the same hospital and the same ultrasonographer to perform follicle monitoring, you can avoid the objective measurement error of medical instruments and the subjective judgment error of the ultrasonographer.