Patient's question:
I have a friend who is careful every time she gets pregnant, but she still loses it.Doctor's answer:
(1) Time of Follicular Development: At the beginning of each menstrual cycle, multiple follicles develop simultaneously, but generally only one or two develop to maturity, known as the dominant follicle (leading follicle), while the remaining follicles undergo atresia. Some authors report that in over 90% of cycles, only one follicle grows rapidly to maturity, with 5% to 11% having two dominant follicles develop. Follicular ultrasound imaging can be performed as early as day 5 to 7 of the menstrual cycle, with the smallest detectable diameter being 4 to 5 mm.(2) Follicular Growth Rate: Ultrasound can detect small follicles in the ovaries between days 3 to 5 of the menstrual cycle, which gradually grow larger. On average, the follicles reach their maximum size around day 14, at which point ovulation may occur. From day 5 to the day before ovulation, the dominant follicle grows by an average of 1.5 mm per day. By day 10, it grows by an average of 1.2 mm per day, and by the day before ovulation, it grows by an average of 1.9 mm per day, reaching maturity.
Mature follicles exhibit the following characteristics:
① The follicle appears round or oval, with a diameter of 15 to 30 mm (21.2 ± 0.53 mm). The follicular cavity is anechoic, clear, and pure, with well-defined boundaries and a thin wall.
② In approximately 20% of mature follicles, the cumulus oophorus can be observed one day before ovulation, appearing as short, strong echoes near the wall of the follicle.
(3) Ultrasound Imaging of Follicles Near Ovulation:
① The cumulus oophorus appears in about 20% of follicles, mostly in those >18 mm in diameter, indicating that ovulation is likely to occur within 24 hours.
② A (acoustic halo) around the follicle, formed as the LH level rises, causing edema in the theca tissue and the separation of granulosa cells from the theca layer, also indicates that ovulation is likely within 24 hours. Currently, this feature is rarely observed on ultrasound.
③ The granulosa cells and the inner layer of the theca tissue completely separate, and the follicular wall shows a dentate change, indicating that ovulation will occur within 6 to 10 hours. This feature is extremely rare to observe on ultrasound. Some authors suggest that mature follicles with a diameter of 18 to 25 mm have a higher pregnancy rate.