Human reproduction depends on a sperm cell fertilizing an egg cell. Sperm cells are produced in the testes of males while the egg cell (ovum) is released by the ovaries in females. The entire process of producing and releasing these cells (collectively known as gametes) in the male and female body is a carefully coordinated process. Both the sperm cell and egg cell contain half the genetic material of the parent, which when combined forms an embryo that is composed of cells with a complete genetic blueprint.
What does ovulation mean?
Ovulation is the process by which the ovary releases an egg cell (ovum). This happens once in every menstrual cycle, which is approximately once every 28 days. However, for some women ovulation may occur more frequently while for others it may be less frequently. Ovulation is necessary for pregnancy to occur but there is a window during which this is possible.
If the egg cell is not fertilized within a few das after ovulation then the egg cell along with the thickened inner wall of the uterus (endometrium) is shed and removed from the uterus. This occurs during menstruation. The ovaries and uterus prepares for the ovulation, pregnancy or menstruation with the next cycle. However, in some women ovulation does not occur during the menstrual cycle. This is known as anovulation or an anovulatory cycle.
Read more on menstrual cycle.
Why does not ovulation not occur?
Anovulation (the absence of ovulation) can occur for several reasons. Sometimes more than one cause is present at the same time. However, in most cases anovulation can be isolated to one condition or factor. The lack of ovulation is not always associated with the lack of menstruation. Many women may menstruate like clockwork but this does not mean that ovulation occurs with every menstrual cycle.
Ovulation is dependent on ovarian health as well as the stability of a normal menstrual cycle. Eventually ovulation does cease in life, sometimes well before menopause sets in. Many women may not be aware when ovulation has ceased or when ovulation is or is not occurring from one menstrual cycle to another. Therefore it is important to conduct the necessary investigations to confirm ovulate, despite the regularity of menstruation.
Read more on how to know when you are ovulating.
There are several diseases of the ovaries that can affect its normal function, like releasing an egg cell during the ovulation phase of the menstrual cycle. This includes injury to the ovaries (physical, chemical or electromagnetic), benign tumors, cancer of the ovaries, cysts in the ovaries (polycystic ovarian syndrome), scar tissue in the ovaries amd failure of the ovaries to function normally (premature ovarian failure) due to other causes like genetic defects, autoimmune syndromes and sometimes due to unknown causes.
A ovarian follicle containing an egg cell has to rupture in order to release the egg cell. This is a carefully coordinated process which is facilitated by sex hormones, like follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen and progesterone. When there are problems with these hormones then ovulation may be disrupted or it may not even occur (anovulation).
These types of hormone problems are seen with polycystic ovarian syndrome (PCOS), pituitary gland problems, hypothalamic disorders and excessively high levels of prolactin. However, it can also occur when there are problems with other hormones and glands, including thyroid disorders, adrenal insufficiency, Cushing syndrome and high levels of insulin which may be seen in several conditions, including type 2 diabetes mellitus.
Certain hormone contraceptives, like the birth control pill, block ovulation. This is done for purpose of preventing pregnancy although hormone contraceptives may also be sometimes used to treat other conditions. These hormone contraceptives achieve blocking ovulation by altering the hormone fluctuations that occur with a normal menstrual cycle and which are responsible for stimulating the ovary to release an egg cell.
The main way that these contraceptives work is by increasing the levels of estrogen and progesterone which should occur with pregnancy and therefore the body “blocks” ovulation. It is important to stress that in these cases anovulation is desired in order to prevent pregnancy. Once contraceptives are stopped then ovulation should be resumed. However, this may not always occur an ovulation may take months before it occurs again after using hormone contraceptives.
Starvation and Eating Disorders
Ovulation is a normal part of the menstrual cycle but disturbances in general health status can affect the cycle and therefore ovulation. Nutritional problems are one such possible cause as it impacts overall health and wellbeing. Therefore anovulation (no ovulation) may be seen with starvation. Apart from famines, starvation are more likely to be seen with extreme dieting. It can also occur with eating disorders such as anorexia nervosa.
Obesity is another major factor in anovulatory cycles (menstrual cycles where ovulation does not occur). The excess body fat can affect the female hormone levels which can disrupt ovulation. It can also affect the body’s response to insulin (insulin resistance) which causes the pancreas to increase insulin levels (hyperinsulinemia). This can also impair ovulation. The global obesity epidemic may be one of the main reasons for rising infertility rates globally.
Anovulation (no ovulation) and even amenorrhea (no menstruation) can occur with excessive exercising. This is more likely to be seen among professional female athletes. Although exercise has a host of benefits and may even help restore ovulation in women with anovulatory cyles associated with conditions like polycystic ovarian syndrome (PCOS), exercise that is excessive can have the opposite effect. It interrupts the body’s metabolic activity and disrupts the hormonal cycles necessary for ovulation and menstruation.
Stress is any strain that is placed on the body. This can be physiologic stress which may occur with severe illness. It can also occur psychological stress. Both can affect ovulation. The role of mental health was often overlooked as a factor in reproductive health. However, research has revealed that it plays an important part and may therefore contribute to anovulation. It can also disrupt the menstrual cycle apart from impacting on ovulation.