Polycystic Ovary Syndrome (PCOS) is a common hormonal disorder affecting women of reproductive age. It is characterized by a hormonal imbalance that can lead to irregular or absent menstrual periods and excess levels of androgens. Diagnosing PCOS typically involves a combination of clinical symptoms, blood tests to check hormone levels, and a pelvic ultrasound. The ultrasound is a necessary tool for visualizing the ovaries, which is a key component of the international criteria used to confirm the condition.
Why Ultrasound is Used for PCOS Diagnosis
The primary purpose of the ultrasound in a PCOS workup is to assess the physical appearance of the ovaries, a feature known as Polycystic Ovarian Morphology (PCOM). The ultrasound provides a visual of the ovaries, allowing a healthcare provider to count the small, fluid-filled sacs, or antral follicles, present on the surface. These follicles measure between 2 and 9 millimeters in diameter and represent eggs that have not matured and been released due to the hormonal imbalance associated with PCOS.
Current guidelines suggest that an ovary is considered polycystic if it contains 20 or more of these small follicles, a metric known as the Antral Follicle Count (AFC). The ultrasound also allows for the measurement of Ovarian Volume. Volume is considered increased if it exceeds 10 cubic centimeters (mL). The presence of either an increased follicle count or a large ovarian volume in at least one ovary contributes to the diagnosis of PCOM, which is one of the three criteria used to confirm PCOS.
Determining the Ideal Timing for Diagnosis
The most accurate information is obtained when the ovaries are in a state that is least influenced by the normal hormonal fluctuations of a menstrual cycle. For women who experience regular periods, the ideal time for a diagnostic ultrasound is during the early follicular phase, typically between Day 2 and Day 5 of the cycle. During this time, the uterine lining is thin, and no dominant follicle has begun to develop, ensuring the small antral follicles are clearly visible and can be accurately counted.
Performing the scan later in the cycle can lead to an inaccurate assessment. A growing dominant follicle (a fluid-filled sac larger than 10 millimeters) or a corpus luteum from a recent ovulation can obscure the view of the smaller antral follicles. These larger structures can also falsely increase the calculated ovarian volume. If a dominant follicle or corpus luteum is present during the scan, the ultrasound must be repeated during the next cycle to ensure diagnostic accuracy.
For women who have irregular or absent periods, the timing for the ultrasound becomes less straightforward. In these cases, the scan may be performed at a random time, but the primary goal remains to rule out any functional cyst or recent ovulation that could interfere with the results. A common practice is to perform the ultrasound shortly after a progesterone withdrawal bleed. This mimics the start of a menstrual cycle and ensures the ovaries are in a quiet state for counting the antral follicles.
Timing Considerations During Fertility Treatment
Once a diagnosis of PCOS is established and a patient begins fertility treatment, the timing and purpose of the ultrasound change significantly. These scans are used for active monitoring, often referred to as follicle tracking. The goal shifts to tracking the growth of a dominant follicle in response to fertility medications like clomiphene or letrozole, which are used to induce ovulation.
This monitoring requires serial ultrasounds that are scheduled dynamically. They often start around Day 10 of the cycle or a few days after medication begins, and are repeated every one to three days. The healthcare provider is looking for a follicle to mature, typically reaching a size of 18 to 24 millimeters, which indicates readiness for ovulation or a trigger shot. The scans also measure the thickness of the uterine lining, or endometrium, which needs to be at least 7 to 8 millimeters thick to be receptive to a potential pregnancy.
Preparing for the Ultrasound
Preparation for the ultrasound depends on the specific type of scan being performed. A transvaginal ultrasound is the preferred method for assessing PCOM because it provides the clearest, high-resolution images of the ovaries. For this scan, a slender probe is gently inserted into the vagina, and the bladder must be empty. An empty bladder allows the probe to get closer to the pelvic organs for optimal visualization.
A transabdominal ultrasound, where the probe is moved across the lower abdomen, may be used for younger patients or those who have not been sexually active. This approach requires the patient to arrive with a comfortably full bladder. The fluid helps to push the uterus and ovaries into a position that is easier to visualize through the abdominal wall. Patients should wear comfortable, loose-fitting clothing, ideally a two-piece outfit, and bring a record of their last menstrual period and any recent blood test results to provide the most complete clinical picture for the healthcare team.