Ultrasound Use for PCOS Diagnosis

A transvaginal ultrasound can spot follicles on the ovaries

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When a transvaginal ultrasound is done for suspected PCOS, or polycystic ovary syndrome, it's to see whether there are an excessive number of small follicles on the ovaries—a hallmark of the condition. This imaging test involves placing a probe in the vagina to view these organs from the inside.

While ultrasound alone isn't enough to confirm PCOS, results are an important part of the diagnostic puzzle. A healthcare provider will also take your medical history, a physical examination, and blood test findings into account.

This article discusses transvaginal ultrasound for PCOS. It explains how this type of imaging is performed and what your healthcare provider is looking for.

A gynecologist sets up an ultrasound machine. A transvaginal ultrasound scanner of the internal organs of the pelvis. Female health concept
Kateryna Kukota / Getty Images

How Is a Transvaginal Ultrasound Performed?

A transvaginal ultrasound can be performed in a healthcare provider's office. For the procedure, you may be asked to drink up to 42 ounces of fluid before your test to fill your bladder, making it easier to see your ovaries. 

A lubricated ultrasound probe is placed inside the vagina, which transmits an image of the internal organs onto a screen. An ultrasound technician then measures and takes pictures of your ovaries and shares them with your healthcare provider. 

Does a Transvaginal Ultrasound Hurt?

Some individuals may experience very mild discomfort while the technician pushes down during the ultrasound. This depends on the ease with which the sonographer can locate the internal reproductive organs.

Diagnosing Polycystic Ovary Syndrome (PCOS)

PCOS is is essentially an imbalance of sex hormones. It is characterized by high levels of androgens, male hormones like testosterone.

Since these hormones are involved in the regulation of bodily processes ranging from reproduction to metabolism, the condition can lead to a wide variety of signs and symptoms of PCOS.

The first step when evaluating your symptoms, exam and laboratory findings is to exclude other disorders which might cause these findings.

These conditions (which may appear similar to PCOS but are different) include:

Differentiating PCOS from thyroid disease is made more difficult in that some forms of thyroid disease are more common in people with PCOS, and some of the tests used to diagnose thyroid disorders are inaccurate in people with PCOS.

PCOS Diagnostic Criteria

The Rotterdam Criteria, the current diagnostic criteria for PCOS, requires two of the following (with the exclusion of other causes):

  1. Absent or irregular menstrual cycles (eight or fewer periods in one year). Since only two of these three criteria need to be met, there are some who will meet the criteria for a diagnosis of PCOS despite having regular monthly menstrual cycles.
  2. High androgens on blood work or signs of high androgens in the body such as acne, excessive hair growth (hirsutism), or male pattern hair loss (androgenic alopecia). Blood tests often reveal elevated testosterone and free testosterone levels as well as dehydroepiandrosterone sulfate (DHEAS) levels.
  3. The presence of follicles—commonly and erroneously referred to as cysts—on an ultrasound (see clarification below). Some criteria define PCOS as having 12 or more small follicles that are between 2 and 9 millimeters (mm) in diameter in both ovaries. However, in the United States, healthcare providers do not typically rely solely on that definition in order to make a diagnosis.

It is possible to have cystic ovaries without symptoms of hyperandrogenism. It is also possible to be diagnosed with PCOS without having "classically cystic" ovaries.

Studies suggest that measuring anti-Mullerian hormone levels may be a useful substitute for transvaginal ultrasound in some cases for the diagnosis of PCOS.

Ultrasound for Diagnosing PCOS

A transvaginal ultrasound is used to examine internal structures in assessing for PCOS. The sonographer will examine your uterus, cervix, and uterus. The number of follicles on your ovary will be counted to yield what is known as an antral follicle count (AFC).

What Are Antral Follicles?

Antral follicles are resting follicles that are found in the ovary at the beginning of each menstrual cycle. They are approximately 2 to 9 mm in size, which is less than half an inch.

A high antral follicle count indicates a large number of eggs that remained in the ovary instead of being released. This may indicate PCOS.​

Cysts vs. Follicles in PCOS

Both cysts and follicles are more common in people with PCOS than those without the condition. Many confuse cysts with follicles.

Despite its name, the ovaries in PCOS don't produce an overabundance of cysts. It is actually an excessive number of follicles that is part of the diagnostic criteria.

A name change for PCOS has been proposed to clear up confusion and properly educate health professionals and consumers. 

People with PCOS tend to produce follicles, which are small collections of fluid in the ovary and are the result, not the cause of, the imbalance of sex hormones. Each month, the ovary produces follicles that mature and are released into the fallopian tube.

Because of the hormone imbalance in PCOS, these follicles don't mature and don't get released by the ovaries, which often leads to infertility.

Who Diagnoses PCOS?

PCOS can be diagnosed by a gynecologist, endocrinologist, or reproductive endocrinologist.—medical specialists with additional training in evaluating and treating hormonal disorders.

If you are uncertain about your diagnosis of PCOS (or lack of one), it can’t hurt to get a second opinion. Check out the American Society for Reproductive Medicine or the Androgen Excess and PCOS Society for a local recommendation.

A Word From Verywell

The diagnosis of PCOS can be time-consuming and frustrating. Other conditions which can cause similar symptoms need to be ruled out first, and then symptoms such as menstrual abnormalities and evidence of androgen excess are evaluated.

Transvaginal ultrasound can provide important information about follicles (as opposed to cysts which has led to much confusion over the years.) The measurement of the anti-Mullerian hormone may provide a substitute for ultrasound in some circumstances.

Once a diagnosis is made, the treatment options for PCOS can be reviewed in order to help you cope with the many annoying (and sometimes serious) consequences of the condition.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  4. Dewailly, D. Diagnostic criteria for PCOS: Is there a need for a rethink?. Best Practice and Research. Clinical Obstetrics and Gynaecology. 2016. 37:5-11. doi:10.1016/j.bpobgyn.2016.03.009

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By Nicole Galan, RN
Nicole Galan, RN, is a registered nurse and the author of "The Everything Fertility Book."