The Menstral Cycle
The menstral cycle is often referred to as the ovulation cycle, when treating infertility in females. A hormone imbalance in women will effect the monthly cycle to the degree that it may influence ovulation or the luteal phase
For those wondering how this evolves month after month, the information that follows will provide an account of the hormonal influences that make up the monthly cycle. The information will also provide an insight in to the fertility drugs used during ART and the effect on the reproductive system, responsible for conception.
The graph is an indication of the hormone activity in a normal cycle, before and after ovulation, into the next cycle, with no pregnancy. The example is a typical 28 day cycle, on a background of charting daily activities in a monthly cycle.
The monthly cycle
The principle goal of a cycle is to produce an egg, capable of being fertilized, as well as the conditions necessary to nurture it for the conception and the duration of a pregnancy.
Menstruation is the actual shredding of the endometrium, the lining of the uterus. If no pregnancy takes place, the endometrium is shred at the beginning of a new cycle, in order to restart the process of a new ovulation and possible pregnancy.
There are a number of hormones which perform a primary function, necessary for pregnancy. Each one has it's own unique function, and together work towards that ultimate goal. While the reproductive system has many hormones, here are the most important ones influencing fertility:
Estrogen: There are three types of estrogen, one of the main one's being estrodial. Produced by the follicles that develop inside the ovaries, from menstruation to ovulation. The main function is the maturing of the eggs and uterine lining and the fertile quality of the cervical fluid, when approaching ovulation. Estrogen builds up from the beginning of the cycle.
Follicle Stimulating Hormone (FSH): The hormone responsible for the initial development of a few follicles each cycle. A number of follicles will evolve from tiny and immature eggs, into the large and mature ones which are released. FSH is produced by the pituitary gland found in the base of the brain. Like estrogen, this hormone builds up from the beginning of the cycle till its peak at ovulation.
Luteinizing Hormone (LH): This is another major hormone produced by the pituitary gland. The function is twofold, for stimulating and completing follicular growth (together with FSH), as well as luteinization of the ruptured follicle, for it to transform into a corpus luteum, once ovulation has taken place. Nearing ovulation, the LH increases rapidly, referred to as the "LH surge". This surge is the trigger for ovulation, which will take place a day or so later. FSH and LH together form part of the pituitary or gonadotropin hormones. LH also builds up from the beginning of the cycle.
Gonadotropin Releasing Hormone (GnRH): The hormone produced by the hypothalamus, which causes the pituitary to increase the production of the gonadotropin hormones, FSH and LH. The hypothalamus is situated just above the pituitary and forms part of the walls of the lower brain. Stress and life style conditions, affect the hypothalamus and its production of GnRH. It is for this reason that the cycle can be affected by stressful conditions, thus changing the length of the cycle. The output of FSH and LH is directly affected by the hypothalamus and if it is under stress, then so are the correct levels of FSH and LH, which controls the length of the first phase of the cycle.
Progesterone: The hormone produced by the corpus luteum, and responsible for the thermal shift in raised temperature. The heat inducing hormone. Progesterone is responsible for that so important function of nurturing and maintaining of the endometrium lining of the uterus in the luteal phase, or post ovulatory phase. The corpus luteum, the follicle body from where the egg is produced and left behind on the inside of the ovarian wall, will disintegrate with no pregnancy, triggering the progesterone levels to decrease, and thus the start of menstruation process. While the levels of progesterone are high, no further hormones will be release, therefore no follicles will develop and no further ovulation will be possible. This is the body's protection mechanism when pregnancy takes place, as it feeds the corpus luteum, sustaining the developing fetus, until the placenta takes over. Progesterone and infertility - a hormone necessary to protect and sustain the fertilized egg.
Length of cycle
The menstral cycle, when perfect, is deemed to be 28 days in length. What follows would be a perfect day of ovulation on day 14. Under this assumption, having sperm meet egg on day 14 should result in conception.
Factors affecting the length of the cycle are generally experienced in the pre ovulatory, or first phase of the ovulation cycle. These factors can affect the production of FSH and LH. When this happens, ovulation would be delayed. Under such conditions, the length of the cycle would change. Ovulation calendar provides examples of the different cycle lengths, resulting from any disruptions experienced in the pre ovulatory phase.
For woman with a short luteal phase, the third phase of the cycle, progesterone levels may be the cause. So even when all the conditions leading up to that point have been perfect, conception may result in a miscarriage due to an inadequate luteal phase.
Every hormone in the menstral cycle has an influence on conception and sustaining a healthy pregnancy.
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