Ovulation problems are a common cause of subfertility and gynaecological problems. To understand problems and difficulties with ovulation it is important to understand how normal ovulation works.
Ovulation is defined as the production of an egg, preferably on a cyclical basis. This monthly production of an egg, which allows pregnancy in the female, is controlled by a number of factors.
Steps in a natural ovulation cycle
Step 1. Messages to the ovary
A higher thinking centre of the brain (the hypothalamus) sends a messenger chemical called a hormone to a gland in the centre of the brain (the pituitary gland). This messenger chemical is called GnRH and its role is to release a second set of messenger hormones from the pituitary gland, which will travel to the ovary.
Step 2. Two hormones are released
The pituitary gland is a small 1½ cm diameter gland situated in the centre of the brain. It releases hormone messengers that control many functions in the body such as the thyroid gland, the adrenal gland, and breast milk production. It releases two important hormones that control both egg production and release in the ovary:
(a) FSH (follicle stimulating hormone):
This messenger hormone travels from the pituitary gland to the ovary and tells the ovary to grow an egg or eggs.
(b) LH (luteinising hormone):
For 2 days out of every 28 days this hormone is produced in large quantities and travels from the pituitary gland to the ovary and tells the ovary to ripen and then release the egg. LH levels only increase in the bloodstream 36 to 44 hours prior to egg release. The sudden spike of LH released by the pituitary gland is called a “surge”. It’s rather like a “sneeze” of hormone being released. Daily blood levels can be used in patients to predict this LH surge and therefore predict the time of egg release to within a couple of hours. This technique is widely used to help infertile patients become pregnant by telling them when to time their intercourse or artificial insemination.
Step 3. Egg development and maturation
All the eggs present in the ovary for a woman’s lifetime are actually produced when she is still a foetus inside her mother. As she enters puberty she has approximately 400,000 eggs in her two ovaries. When all the eggs are used up and there are none left to proceed to maturity each cycle, the female goes into menopause. This happens at an average age of 52 years.
From puberty, at the start of each menstrual cycle up to 400 eggs are stimulated by the release of FSH from the pituitary gland. In the context of the normal 28-day cycle this usually occurs between Day 1 and Day 5 of the cycle, while often the period is still occurring. Each of the eggs develops in a very small cyst called a follicle. These follicles all begin to grow under the influence of FSH. However, it would clearly be very undesirable for 30 to 50 eggs to be released every cycle. This would make the risks of multiple pregnancy far too high.
The body and the ovary therefore have a mechanism of selecting only one (and sometimes two) follicles to become the selected egg, which will grow onto maturity for that month. This process of egg selection and its subsequent growth to a mature egg occurs between Day 5 and Day 12 of the average 28-day cycle. As this dominant follicle and egg grow, the other numerous little follicles, which started to grow, fade away and the primitive eggs die off, never to be used.
During this phase of egg development and maturation, cells in the wall of the developing follicle/cyst start to produce a hormone called oestrogen. Oestrogen is the most important female hormone and it is possible to measure its daily rise in the bloodstream from Day 5 to Day 14 in parallel with the egg development. Typically a single follicle producing a single egg will have a peak oestrogen level about one day prior to ovulation of 400 to 1400 p.mols per litre.
Step 4. Ovulation.
The release of the now mature egg occurs usually between about Day 12 and 15 of the average cycle. The pituitary gland releases a rapid spike of LH messenger hormone which travels to the ovary and starts a complex series of chemical actions which ripen the egg, detach it from the wall of the cyst/follicle in which it is growing so that it is now floating free in the fluid in the follicle. Finally the follicle splits open to release the egg.
The egg is hopefully picked up by the waiting fallopian tube and if intercourse or insemination occurs around this time, sperm and egg may meet together in the fallopian tube and a pregnancy may result.
Step 5. Progesterone is produced
After ovulation the follicle reforms and the cells in the lining of a follicle change their chemical structure and begin to produce a hormone called progesterone. The follicle that has just released the egg is now called a corpus luteum. Progesterone is a very important hormone, which travels from the corpus luteum to the uterus and changes the lining of the uterus preparing it to receive a pregnancy. This second half of the menstrual cycle is therefore called the luteal phase of the menstrual cycle and would typically run from day 14 to day 24 of the normal cycle.
If the female does not become pregnant in this particular cycle the corpus luteum cyst will degenerate around 14 days after ovulation (day 28 of the cycle) and as the progesterone levels drop the lining of the uterus becomes unstable and the period will begin.
If, however, pregnancy has occurred the pregnancy itself begins to send special hormonal messengers to the corpus luteum telling it not to degenerate. The corpus luteum continues to produce progesterone past day 28 of the cycle and no period occurs. The lack of the menstrual period therefore serves as a marker that the patient may be pregnant and several days later a pregnancy test can be performed.
Find out more about treatments for ovulation disorders.