Follicle size on the 18th day of menstruation

Many girls only know about menstruation, but don’t know what causes it. In fact, menstruation is caused by the shedding of the endometrium, and with the menstrual cycle, the follicles in our body will also undergo related changes. Some people still face the risk of pregnancy when having sex during the safe period. This is because women will have ovulation behavior when they are excited, which will lead to contraceptive failure. So, what is the size of the follicle on the 18th day of menstruation?

(1) Time of follicle appearance: At the beginning of each menstrual cycle, multiple follicles develop simultaneously, but generally only one or two follicles develop to maturity, called the primary follicles (dominant follicles), and the remaining follicles close one after another. Some authors have reported that in more than 90% of the cycles, only one follicle grows rapidly to maturity, and 5%-11% have two main follicles develop. The earliest time for ultrasound imaging of follicles can be 5-7 days in the menstrual cycle, and the minimum diameter displayed is 4-5mm.

(2) Follicle growth rate: Ultrasound can be used to detect small follicles in the ovaries on the 3rd to 5th day of the menstrual cycle. These follicles gradually grow larger and reach their largest size on the 14th day on average, during which time ovulation can occur. From the 5th day of menstruation to before ovulation, the primary follicle grows an average of 1.5mm per day; before the 10th day, it grows an average of 1.2mm per day; 4 days before ovulation, it grows an average of 1.9mm until the follicle matures.

Mature follicles may show the following characteristics: ① The follicles are round or oval, with a diameter of 15-30mm (21.2+-0.53mm), and the follicles are echo-free, clear and pure, with clear boundaries and thin walls. ② One day before ovulation, 20% of the mature follicles can be seen as a cumulus oophorus image, which appears as a short and strong echo near the wall of the follicle.

(3) Ultrasound images of follicles near ovulation: ① The appearance rate of cumulus ovum is about 20%, mostly appearing in mature follicles >18mm, predicting ovulation to occur within 24 hours. ② The sonic ring around the follicle is formed as the LH value rises, the membrane tissue edema, and the granulosa cells separate from the theca cells. Ovulation is predicted to occur within 24 hours. Ultrasound currently shows that the chance is very low. ③ The granulosa cells of the follicle wall are completely separated from the bottom layer of the membrane tissue, and the follicle wall appears serrated.