PCOS and Polycystic Ovaries

What is the link between PCOS and Polycystic Ovaries?

According to the 2023 International Evidence-Based Guidelines for the Assessment and Management of PCOS, polycystic ovaries, a condition where multiple immature follicles build up on the ovaries (sometimes referred to as a “string of pearls”), is one of the core features of PCOS.

Despite the name, some studies have found that only 17-33% of individuals with PCOS have polycystic ovaries.[1] Polycystic ovaries occur when multiple small, fluid-fills sacs (follicles) form but do not get released via ovulation and therefore remain within the ovary. In this article we explore the link between PCOS and polycystic ovaries.

A typical menstrual cycle relies on a complex interplay of chemicals over a cycle of around 28 days and comprised of four key phases:[2]

Menses: the uterus sheds its lining if pregnancy hasn’t occurred from day 1 of the cycle for a typical period of 3-7 days;
Follicular: overlapping with menses and lasting for 10-14 days, the lining of the uterus is restored and follicles in the ovaries grow to produce (usually) a single mature egg or ovum;
Ovulation: at roughly day 14, an eggs is released; and
Luteal: from day 15-28 the egg travels to the uterus and, if fertilized by a sperm, implants into the uterine wall.

The hormonal imbalances associated with PCOS can interfere with the follicular phase, resulting in no one single dominant mature egg or ovum developing:[3][4]

The hypothalamus (a region of your brain) releases gonadotrophin-releasing hormone (GnRH), a chemical messenger that is vital to puberty, sex drive and fertility;[5]
In individuals with PCOS, the activity level (pulse frequency) of one of the hormones produced in the hypothalamus, the GnRH, is over-active;[6]
The GnRH triggers the pituitary gland (a gland at the base of the brain) to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH);
Between day 6 and 14 of the menstrual cycle, FSH causes follicles, small sacs of fluid in your ovaries that contain a developing egg or oocyte, in one ovary to begin to mature;
Between day 10 and 14, a dominant follicle emerges that out-competes the other follicles for FSH;
This dominant follicle then secretes inhibin that reduces FSH production in effect “turning off” neighboring follicles;[7]
This mature follicle develops into a fully mature egg, within what is now known as a Graafian follicle,[8] and reaches up to 2.5 cm in diameter;[9]
Instead, in individuals with PCOS, elevated levels of GnRH in individuals with PCOS can result in over-production of LH,[10] so that follicle development stalls at the antral phase (2-9 mm in diameter)[11] and no dominant follicle emerges;
In some individuals with PCOS these immature follicles can accumulate and remain as several small follicles often referred to as a “string of pearls”[12], hence the naming of the condition as polycystic ovarian syndrome (PCOS).[13]

The hormonal imbalances associated with PCOS can therefore interfere with the process of ovulation itself:[14][15]

In a typical cycle, the Graafian follicle moves towards the surface of the ovary and, at around day 14, the mature follicle produces sufficient estradiol to trigger an LH surge which kicks off the steps towards ovulation;
In an individual with PCOS none of the small immature follicles is typically capable of growing to a size that would be sufficient to trigger this LH surge.[16]

As a result, PCOS is associated with polycystic ovaries.

The type of cysts formed due to PCOS are, in some ways, not true cysts as they are small immature follicles. Functional cysts formed as part of a typical menstrual cycle are either follicular (halfway through menstrual cycle) or corpus luteum (after release of egg) and grow up to 2-3cm and then usually disappear on their own within 3 months.[17] There are a variety of other types of cysts:[18]

Dermoid cysts or teratoma: usually benign (non-cancerous) cyst that forms from reproductive cells and can contain tissue such as hair, skin or teeth;
Endometrioma: cyst that forms from tissue attaching to ovary in endometriosis; and
Cystadenoma: cyst that develops from cells on the surface of the ovary and can be filled with watery fluid or pus and grow very large.

[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC4341818/

[2] https://my.clevelandclinic.org/health/articles/10132-menstrual-cycle

[3] https://my.clevelandclinic.org/health/diseases/21698-anovulation

[4] https://www.ncbi.nlm.nih.gov/books/NBK279054/

[5] https://my.clevelandclinic.org/health/body/22525-gonadotropin-releasing-hormone

[6] https://www.obgproject.com/2019/06/12/pcos-part-1-sensitive-care-of-the-pcos-patient/

[7] https://www.ncbi.nlm.nih.gov/books/NBK441996/

[8] https://byjus.com/question-answer/what-is-a-graafian-follicle-in-the-ovary/

[9] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/graafian-follicles

[10] https://www.thelancet.com/journals/ebiom/article/PIIS2352-3964(23)00416-4/fulltext

[11] https://advancedfertility.com/infertility-testing/antral-follicle-counts/

[12] https://www.uptodate.com/contents/polycystic-ovary-syndrome-pcos-beyond-the-basics