Ovulation, Menstruation and PCOS: What Goes Wrong?
Fertility and menstruation are two of the key areas of concern for sufferers of PCOS. Ovulation and menstruation are incredibly complex cycles which are controlled by hormones. These hormones can be disrupted by PCOS, resulting in reduced fertility and interrupted menstruation. Through good education, careful management, and medication where appropriate, nearly all PCOS sufferers can achieve normal ovulation and healthy pregnancy. In this article, we will look at what happens during ovulation and what goes wrong with PCOS.
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Ovulation and Menstruation: how does it work?
Before we look at what goes wrong during PCOS, let us first understand what a normal ovulation and menstruation cycle looks like! Ovulation is the process of the ovary releasing an egg that is ready to be fertilised. Menstruation is the process of growing the endometrial lining in the uterus and shedding it if there is no fertilization after ovulation.
The cycle of ovulation begins with menstruation from the previous months cycle. Each ovulation cycle typically lasts between 24 and 38 days. Ovulation typically occurs around day 14. Ovulation is controlled from 4 different centres around the body through the release of different hormones, primarily Leutinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) [source].
The ovaries contain a store of eggs and primordial follicles, which are actually produced during foetal development and stored in the ovaries until puberty! For ovulation to occur, a primordial follicle must come together with an egg and develop into a mature follicle which can then release the egg to be fertilised. For follicle development to happen, multiple primordial follicles are recruited, but only 1 will undergo full maturation. The single follicle that is finally selected is stimulated by FSH, causing it to undergo rapid growth. Once it has grown, FSH levels are reduced, and LH levels are increased. High LH levels cause the follicle to rupture and release its egg outside the ovary [source].
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What’s left of the follicle still plays a very important role. The leftover follicle, called the corpus luteum, starts to release a number of important hormones. Most notably, it releases high levels of progesterone as well as estradiol (a form of estrogen) [source]. Progesterone and estradiol levels are controlled by LH. The leftover follicle will last for about 14 days before regressing. If fertilization occurs successfully, the leftover follicle is actually preserved and will continue to release progesterone throughout the early stages of pregnancy, until the placenta is mature enough [source]. If no fertilisation happens then the cycle will repeat itself .
While the ovulation cycle is happening, another important cycle is occurring in the uterus. The wall of the uterus, called the endometrial lining, undergoes a process of growing and shedding commonly known as the menstrual cycle. The main function of the menstrual cycle is to prepare the uterus to receive a fertilised egg and nurture it through its early growth. The menstrual cycle is mostly controlled by hormones that are released from the ovary during ovulation, such as estrogen and progesterone [source].
Menstruation is divided into three phases: the proliferative phase, the secretory phase, and the menstrual phase [source]. During the proliferative phase, estradiol from the ovaries causes the endometrium to start growing rapidly. Estradiol also causes the new tissues to be more sensitive to progesterone [source]. Progesterone acts as the opposite of estradiol. Progesterone stops the endometrium from growing by removing estrogen receptors and deactivating estradiol [source], this prevents continuous growth of the endometrium, which can become a cancer risk. Around this time, ovulation occurs.
After ovulation, the second phase of menstruation begins, the secretory phase. During this phase, the endometrium begins to mature, becoming rich in energy stores to feed the growing embryo. During this phase, implantation of the egg occurs if conception was successful. If it wasn’t successful, then towards the end of this phase, the blood supply to the endometrium begins to be reduced, in preparation for menstruation [source].
The menstrual phase is the final phase of the cycle. A decline in estrogen and progesterone levels results in the start of menstruation, during which the outer layers of the endometrium come apart and leave the body in liquid form (menstruation) [source].
However, if fertilisation was successful, menstruation does not occur and instead the fertilised egg is implanted into the endometrium, which continues to grow. Progesterone levels remain high, encouraging more growth and some cells will begin to change into what will later become the placenta. Progesterone levels are therefore essential for healthy endometria [source].
Why does PCOS cause infertility?
Now that we understand what happens during normal ovulation, we can take a look at what goes wrong during ovulation for sufferers of PCOS. For women with PCOS, it is common for the ovulation cycle to be stopped while the follicle is still developing, before it can reach the stage where it is mature enough to release an egg. This is known as anovulation. This results in under-developed follicles collecting on the outside of the ovary during each cycle, leading to the appearance of cysts on the ovary (although they are not actually cysts), hence the name Poly-Cystic Ovarian Syndrome [source].
It is important to note that follicle development does not stop because the follicles or eggs are unhealthy, but rather because PCOS causes disruptions in the incredibly complex hormone signalling network that controls ovulation. In fact, studies have shown that simply by adding back the correct amount of FSH, normal ovulation and fertility is completely restored in most PCOS sufferers [source].
“Normal hormone levels have to be restored to induce ovulation. This is achievable for nearly all women with PCOS.”
Because the follicle is stopped before it can reach maturity, an egg is not released from the ovary. This is why many women with PCOS initially have difficulties in becoming pregnant. Normal hormone levels have to be restored through lifestyle treatments or medication in order to induce ovulation. Luckily, this is well documented and easy to achieve for nearly all women with PCOS. Having PCOS does not make you infertile.
Why does PCOS interrupt menstruation?
Because an egg is not released from the ovary, the remains of the follicle do not start releasing progesterone, as discussed above. The lack of progesterone means that there is no signal telling the endometrium to stop growing, which is a major contributor to the cancer risk associated with PCOS. Secondly, because the estrogen and progesterone levels are not as they should be, no signal is sent to the endometrium to begin shedding. In other words, without ovulation, there is no signal to begin menstruation, which is why many women with PCOS do not have a regular menstrual cycle.
Why does PCOS cause anovulation?
Why exactly does ovulation get stopped for women with PCOS? The answer to this is still not fully understood, although there is lots of research happening in this area and a clearer picture is starting to emerge. Let’s take a look at some of the current understanding in this area.
It has been shown that in women with PCOS, levels of FSH are unusually low, which may contribute to why the follicle stops growing. It is thought that the higher levels of estrogen in women with PCOS are what supresses FSH levels [source].
As we previously discussed, during the development of the follicle, it starts to become sensitive to LH. Increasing levels of LH are what cause it to continue maturing and then rupture, releasing the egg. However, in lean women with PCOS, LH levels are typically higher than usual all the time. This abnormally high level of LH actually causes follicles to become sensitive to LH too early, resulting in them prematurely releasing hormones such as progesterone which may stop the follicle from developing [source].
For obese women with PCOS, LH levels are actually in a normal range, however they tend to have lots of excess insulin as they have become insulin resistant [source]. It is thought that excess insulin causes the ovaries to increase their sensitivity to LH, also resulting in the premature release of hormones such as progesterone that stop the follicle from developing. In fact, there is evidence showing that the more resistant the rest of the body becomes to insulin, the more sensitive the ovaries become [source].
Excess testosterone levels in PCOS are known to cause ovulation to pause, however excess testosterone may also cause problems in the release of LH and FSH as well as reducing estradiol production, all of which may contribute to ovulation stopping [source].
“Ovulation can be achieved by restoring FSH levels or reducing excess insulin”
In conclusion, the research now suggests that there are probably two main causes of anovulation due to PCOS. Either through problems with LH and FSH regulation or through problems with the ovary caused by excess insulin and testosterone. Both routes result in a cycle of events that lead to follicles not being able to fully mature, and therefore not releasing an egg. This cycle can easily be broken simply by restoring FSH levels of by reducing excess insulin levels in the case of overweight subjects.
