Almost a third of women with PCOS are estimated to remain undiagnosed while even a larger proportion of those who are diagnosed with it don’t have it at all. Part of the difficulty of diagnosis stems from the reality that PCOS is a syndrome of exclusion meaning doctors must work to rule out other conditions that manifest with similar symptoms.

Some of the most common endocrine problems that physicians must first rule out are hypothyroidism, hyperprolactinemia, and nonclassical congenital adrenal hyperplasia, all of which have symptoms that overlap with those of PCOS but are not in fact PCOS. Once a physician has determined that these are not potential contributors to a patient’s symptoms, the patient may have PCOS if they meet two of the following three criteria known as the “Rotterdam Consensus” criteria:

Clinical and/or Biochemical Signs of Hyperandrogenism

Hyperandrogenism means an excess of male hormones. One way of assessing this is by observation of “excess hair growth” but it is important to note that ideas of what constitutes “excess hair” will vary from one person to another as will the degree to which each individual may seek to address this symptom. A physician will look for signs of excess hair usually along the midline of the body such as over the upper lip, between the breasts, under the navel, along with hair loss or thinning of hair on the scalp, and/or acne.

Lacking these clinical signs does not necessarily rule out hyperandrogenism. Some populations, including Chinese, Japanese, and Korean women do not respond to excess androgens to the same degree as their Caucasian counterparts, for example. In such cases, biochemical methods of assessment—usually a blood test to measure testosterone—will be employed. If you are taking hormonal contraceptives, be sure to speak with your doctor about alternatives, as blood androgen testing will require you to stop about three months in advance.

Oligo and Anovulation

This refers to dysfunctions of ovulation that appear as abnormal menstrual frequency. Oligoovulation describes infrequent ovulation, usually with 8 or fewer periods in a year while anovulation describes a complete lack of a period. Periods that occur more than every 21 days, less frequently than every 35 days, or as abnormally heavy periods, are among the more common ways that this symptom manifests in women with PCOS.

“Polycystic” Ovaries

Again, this terminology is a misnomer as the symptom is in fact referring to an abnormally high number of developing follicles or abnormally enlarged ovaries and not the presence of actual cysts. Regardless of the term, in practice this means that an ultrasound examination of an ovary that reveals either more than 20 developing follicles or a volume in excess of 10 ml qualifies as having a polycystic morphology or form. Since displaying any two of the three characteristics will suffice for a PCOS diagnosis, it is not always necessary for a patient to show polycystic ovaries if they meet the first two criteria.

All of these variables add to the difficulty of diagnosing PCOS, especially in both adolescence and menopause as many of the symptoms have significant crossover with normal signs of puberty and menopause. Take for example a young woman who has had her first period (menarche). It is completely normal for such a person to experience signs of ovarian and adrenal gland awakening, including increased hair growth and androgen excess as well as irregular periods including sometimes-long stretches with no period at all. In more than half of individuals with ovaries, puberty heralds an upregulation of the number of antral or early developing follicles which can sometimes be mistaken for the polycystic ovary appearance. For these reasons, PCOS is likely overdiagnosed in the younger population of women and people assigned female at birth.

Another interesting—and complicating—fact about PCOS is that the irregular periods that can be a hallmark in some patients throughout early life tend to become more regular around the time preceding menopause. Add to this the fact that menopausal women experience relative androgen excess and it points to a murky diagnostic landscape in this age group.