A follicle scan, also known as follicular monitoring, is an ultrasound examination designed to monitor the development of ovarian follicles. Follicles are small, fluid-filled sacs in the ovaries that contain immature eggs. The procedure uses sound waves to create detailed images of the pelvic organs, allowing medical professionals to observe the ovaries and uterus. These scans provide precise data about the progression of a woman’s menstrual cycle, serving as a diagnostic tool in reproductive health.
The Clinical Need for Follicle Tracking
Follicle scans determine whether a woman is ovulating regularly and pinpoint the precise timing of egg release. For individuals trying to conceive naturally, the scans identify the most fertile window for timed intercourse. Monitoring is also employed to assess a patient’s response to fertility medications, such as clomiphene citrate or gonadotropins, which stimulate the ovaries to produce mature follicles.
When a patient is undergoing fertility treatments, the scan guides treatment protocols. For intrauterine insemination (IUI), tracking ensures the sperm is inserted at the optimal moment, just as ovulation is about to occur. In in vitro fertilization (IVF), the scans monitor the growth of multiple stimulated follicles. This monitoring allows the medical team to adjust medication dosages, preventing complications like ovarian hyperstimulation while ensuring the eggs are retrieved at peak maturity.
What Happens During the Follicle Scan Procedure
Follicle scans are performed using a transvaginal ultrasound, which offers a clearer and more detailed view of the ovaries and uterus than an external abdominal scan. During the procedure, the patient lies on an examination table, and a thin, lubricated probe is gently inserted into the vaginal canal. This probe utilizes high-frequency sound waves to transmit images of the pelvic structures to a monitor, allowing the clinician to measure the follicles.
The procedure is quick, lasting five to ten minutes, and is usually painless, though mild pressure may be felt. Since the goal is to observe a dynamic process, the scan is a series of appointments timed throughout the follicular phase of the menstrual cycle. The initial scan is often scheduled around day seven to ten, with subsequent scans repeated every one to three days to track growth and determine maturity.
Understanding the Scan Results
The data collected focuses on three main parameters: the number of growing follicles, the size of the dominant follicle, and the thickness of the endometrial lining. Assessing the number of visible follicles allows the clinician to assess the ovarian response to stimulation and predict the potential number of eggs that may be released. In a natural cycle, only one follicle becomes dominant, while stimulated cycles aim for multiple follicles.
The size of the dominant follicle is the most important measurement for predicting ovulation, as the egg inside is considered mature and ready for release once the follicle reaches a specific diameter. A dominant follicle is ready to ovulate when it measures between 18 millimeters and 22 millimeters. Follicles grow at a predictable rate of about one to three millimeters per day during the late follicular phase, which helps the team pinpoint the day of ovulation.
The scan also measures the thickness and appearance of the endometrial lining. For a successful pregnancy, the lining should measure at least 8 millimeters thick and display a “trilaminar,” or three-layer, pattern by the time of ovulation or egg retrieval. Once the dominant follicle reaches the target size and the lining is receptive, the medical team uses this data to schedule timed intercourse, an IUI procedure, or the administration of a human chorionic gonadotropin (hCG) “trigger shot” to induce the final maturation and release of the egg.