Understanding The Menstrual Cycle

To understand more about the causes of infertility it is important to have some knowledge of the normal menstrual cycle. The most important part of this cycle as far as pregnancies are concerned is ovulation.

Understanding Ovulation

Understanding the process of ovulation can greatly speed up the process of falling pregnant. Girls are born with a large number of eggs in each ovary. Girls have to wait until puberty before ovulation begins. Ovulation occurs when a mature egg is released by an ovary. This occurs approximately once a month for the average woman. Girls will start menstruating during the process of puberty and the date of first menses (a period bleed) is called menarche.

The average woman has a menstrual cycle between 21 and 35 days long. Day 1 of the cycle is defined as the first day of a proper period bleed. The last day is defined as the day before the next period bleed. Although ovulation may occur at any time in the menstrual cycle, there are general rules to determine more accurately when ovulation may take place. Ovulation is thought to occur most often approximately 14 days before the end of a menstrual cycle. At ovulation a woman is at her most fertile. Peak fertility is therefore thought to be approximately 2 days either side of ovulation. Therefore, for a woman with a 23 day cycle, peak fertility would occur during Days 7 to 11. For a woman with a 28 day cycle, peak fertility would occur during Days 12 to 16. For a woman with a 35 day cycle, peak fertility would occur on days 19 to 23.

From the above, it follows that in those women with irregular cycles, the date of ovulation (and therefore peak fertility) cannot be predicted using the time of the cycle alone. Other methods are required to assist in predicting ovulation. These include;

• Measurement of Basal Body Temperature (BBT): your body has the ability to maintain a fairly constant temperature. However, progesterone is released by the ovary during ovulation. This causes a very slightly elevation in BBT by up to 0.5 degrees Celsius. This method is not particularly reliable as this increase is not only small, but also occurs 1-2 days after ovulation. Thus, ovulation may already have occurred before you recognise the temperature elevation. For this reason, it is important to chart your daily temperatures throughout the cycle to see if there are any patterns in your temperature fluctuations which may indicate when ovulation is about to occur.

• Examination of Cervical Mucous: this is a more reliable method of predicting ovulation. The function of mucous produced by the cervix varies during the different stages of the menstrual cycle. The mucous forms a barrier at the entrance of the womb throughout the cycle before and after ovulation to block sperm from entering the womb when there is no chance of pregnancy. But as ovulation approaches, the cervix produces more mucous until at the time of ovulation itself, the mucous becomes stretchy and clear. At this time, the mucous, rather than blocking sperm, actually protects the sperm and aids the sperm to pass through the cervix and onto the egg in the hope that fertilisation may take place.

In an average 28 day cycle, the vaginal and mucous changes may appear as follows;

- Day 1-5: menstruation - blood. - Day 6-9: there is minimal mucous production and the vagina is dry. - Day 10-12: sticky and thick mucous can be seen. This eventually becomes thinner and more white. - Day 13-15: as ovulation occurs, the mucous becomes thinner still, clearer, stretchy and slippery. - Day 16-21: the mucous reverts back to being sticky and thick. - Day 22-28: the vagina becomes drier with little or no mucous.

• Assessing the Position of the Cervix: assessing your cervical position also helps to predict the date of ovulation. This is done by inserting 2 fingers into your vagina and feeling for the location, consistency and wetness of the cervix which is located at the top end of the vagina. Normally, the cervix feels hard and dry. But during ovulation, the position of the cervix changes - it becomes higher. It also becomes softer and wetter to feel.

• Ovulation Predictor Kits (OPKs): in some countries, OPKs can be bought from pharmacies and are particularly useful for women with irregular menstrual cycles. These kits work by detecting luteinising hormone in urine. This hormone is released by the pituitary gland and increases 12-36 hours before ovulation. The kits detect this surge and ovulation is them assumed to be imminent. However, conditions such as Polycystic Ovaries can make these tests unreliable.

What is a Menstrual Cycle?

On average, most women have a regular 28 day cycle. But many women have cycles that are a few days shorter or a few days longer than this. Cycles which last from 21 days to 35 days are deemed to be normal. Even amongst an individual woman, cycle lengths can vary from month to month. A variation of a few days is normal. However, the greater the variation each month, the more difficult it is to predict ovulation (as discussed above).

A normal 28 day cycle looks as follows;

- Days 1-5: Menstrual period or bleed. - Days 6-14: The bleeding subsides as menses ends. At this point, the lining of the uterus called the endometrium is thin. As the days progress, the endometrium thickens in preparation for possible implantation of a fertilised egg. - Days 15-28: The endometrium continues to thicken and prepare for a possible pregnancy. However, if fertilisation has not occurred, the endometrial lining starts to break down and eventually is shed from the rest of the womb causing a period bleed to occur. This happens on Day 1 of the next menstrual cycle and another cycle therefore begins.

But, if fertilisation does take place, the endometrial lining continues to develop. The lining is not shed and therefore no menstrual period takes place (a missed period). Women will obviously relate to this as a sign of pregnancy.

How does the Menstrual Cycle Work?

As has been discussed above, there are a number of hormonal changes that occur at puberty. A region deep within the brain called the Hypothalamus starts to secrete a hormone called Gonadotrophin Releasing Hormone (GnRH). GnRH stimulates a gland located at the base of the brain called the Pituitary Gland which in turn produces another hormone called Follicle Stimulating Hormone (FSH). The presence of FSH in the blood stream triggers the development of eggs in the ovary from follicles (egg sacs).

The follicles once triggered produce oestrogen which signals the pituitary gland to secrete another hormone called Luteinising Hormone (LH). It is the presence of LH that finally triggers the shedding of an egg from an ovary in the process called ovulation. This occurs at around Day 12-15 in the average 28 day cycle.

When the level of LH surges, only the ripest egg sac ruptures to release an egg. This egg then travels along a fallopian tube. If any sperm are present in the fallopian tube, fertilisation may occur. Eggs can be fertilised 12-24 hours after they are shed from the ovary. Sperm can survive inside a woman's reproductive tract for 12-48 hours. Fertilisation therefore does not have to occur immediately after sexual intercourse or ovulation but clearly fertilisation cannot occur in the absence of either.

Once ovulation has occurred, the egg sac remnant transforms into a small yellowish area on the ovary called the Corpus Luteum. This body is responsible for the production of the hormone progesterone which has the effect of increasing blood supply to the lining of the womb in preparation for implantation of the fertilised egg. This whole journey of the egg from ovary to womb takes approximately 5 days. During this time, the fertilised egg continues to undergo cell division and may consist of approximately 150 cells.

In a normal menstrual cycle when there is no fertilisation, the egg starts to degenerate and breakup. The corpus luteum on the ovary shrinks and degenerates also and progesterone levels fall dramatically. This leads to breakdown of the womb lining and contraction of the womb leading to expulsion of all these cells through the cervix and vagina. This causes menstruation which is the blood often called "a period".

This cyclical activity continues to occur in women until they reach the Menopause. At this time, no further eggs are available for ovulation. As a result, the cyclical hormonal activity stops and fertility levels reduce to zero. This winding down of the female reproductive system can take a long time; often women may have symptoms of menopause for a few months to a few years.

What Happens at Puberty in Men?

It is not only women who have dramatic physical and hormonal changes at puberty. Men undergo a similar process but naturally, with very different results. There is no natural cycle in men but an almost continual production of sperm. However, the hormones that control sperm production in men are the same hormones that control the menstrual cycle in women.

Once again, Gonadotrophin Releasing Hormone (GnRH) is released by the hypothalamus at puberty. This triggers the release of Follicle Stimulating Hormone (FSH) from the pituitary gland. FSH stimulates the production of sperm in the testes. At the same time, Luteinising Hormone (LH) is also triggered by GnRH in the pituitary gland. LH stimulates testosterone production in the testes.

The testes release immature sperm called spermatids. These travel through a long coiled tube called the epididymis which may be 40 feet in length. Spermatids mature inside the epididymis and this may take up to 70 days. On ejaculation, mature sperm travel along the vas deferens, through the prostate and other seminal glands where they are mixed with seminal fluid and forced through the penis.

When ejaculation occurs as many as 300 million sperm cells may be released. However, very few will survive the journey through the cervix, uterus and fallopian tubes. Eventually, one single sperm cell will burrow its way into an egg in the fallopian tube. This is fertilisation.

From Surgery abroad with Globe Health Tours.