Your menstrual cycle
You probably already know quite a lot about your menstrual cycle – like how often you get your periods and how heavy they are. In this page we are going to take a more in-depth look at the menstrual cycle, ovulation and periods. Obviously, no website can take the place of talking to a healthcare professional, but this should give you a good general understanding of how it all works.
Understanding your menstrual cycle
The menstrual cycle length (the interval from the first day of bleeding to the next first day of bleeding) is most commonly between 23-35 days. A “normal” cycle can vary from month to month, but usually still falls between this time frame. Any variation in the menstrual cycle is usually due to a change in length of time taken to grow and ovulate the egg (also known as the follicular phase). For most women, the length of time between ovulation (when an egg is released from the ovary) and their monthly period is between 12 to 16 days (this is called the luteal phase).
The menstrual cycle
The first day of your menstrual cycle is the first day of your period (day 1 of full flow). The period usually then lasts from 3 to 7 days. You’ll probably find that if you get period pains, they’ll be at their worst in the beginning of your menstrual cycle. This is because the hormones in your body are causing your uterus (womb) to actively shed the lining that was built up in the previous menstrual cycle.
Preparing for ovulation
At the beginning of your cycle follicle-stimulating hormone (FSH) is produced by the pituitary gland in your brain. This is the main hormone involved in stimulating your ovaries to produce mature eggs. Follicles are the fluid-filled cavities in your ovaries. Each follicle contains one undeveloped egg. The FSH stimulates a number of follicles to develop and start to produce the hormone estrogen. Your level of estrogen is at its lowest on the first day of your period. From then on, it starts to increase as the follicles grow.
While a number of follicles initially begin to develop, normally only one follicle becomes “dominant” and this egg matures within the enlarging follicle. The remaining follicles do not continue to grow and gradually disappear. At the same time, the increasing amount of estrogen in your body makes sure that the lining of your uterus (called the endometrium) is thickening with nutrients and blood. The goal is to create the optimal environment for the fertilised egg, making sure it will have all the nutrients and support it needs to grow. High estrogen levels are also associated with the appearance of ‘sperm-friendly’ mucus that is produced by the cervix (also called fertile cervical mucus). You may notice this as a thin, slippery discharge that may be cloudy white in color. Sperm can swim more easily through this type of mucus and can survive in it for several days.
Your body produces hormones which control your menstrual cycle. At the start of your cycle one important hormone is follicle stimulating hormone [FSH]. The rise in FSH stimulates the follicles in your ovaries [fluid filled cavities that each contain one undeveloped egg] to develop and to start to produce another hormone called estrogen. For illustration purposes only
Understanding the ovulation cycle
The level of estrogen in your body is still increasing and it eventually causes a rapid rise in luteinizing hormone (the 'LH surge') from the brain. This LH surge causes the dominant follicle to rupture and release the mature egg from the ovary, from where it enters the fallopian tube. This process is known as ovulation.
Many women think that they ovulate on day 14, but 14 is an average, and most women will actually ovulate on a different day of the menstrual cycle. Your day of ovulation may vary from cycle to cycle. Some women claim to feel a twinge of pain when they ovulate, but many feel no sensation at all and there's no other sign that you are ovulating.
The level of estrogen in your body is still increasing and at a certain level it causes a rapid rise in LH [LH 'surge']. This LH surge triggers ovulation, where an egg is released from the ovary. Although many women think they ovulate on day 14, the actual day of ovulation will vary depending on your cycle length. Some women feel a twinge of pain when they ovulate.For illustration purposes only
Once the egg has been released, it moves along the fallopian tube towards your uterus. The egg can live for up to 24 hours and sperm can survive in the uterus for 3-5 days. So the days leading up to ovulation and the day of ovulation itself are your most fertile – when you are most likely to get pregnant. As soon as you have ovulated, the follicle starts producing another hormone called progesterone.
Progesterone causes further build up of the endometrial (uterus) lining in preparation for a fertilised egg. Meanwhile, the empty follicle within the ovary, called the corpus luteum, starts to shrink, but continues to produce progesterone and starts to produce estrogen. You may get pre-menstrual symptoms (PMS) such as breast tenderness, bloating, lethargy, depression and irritability at this stage due to these hormones.
Once the egg has been released it moves along the Fallopian tube towards your womb. The egg lives for 12-24 hours, but because sperm can live for several days you are at your most fertile and most likely to get pregnant if you have sex without contraception on the day that you ovulate or the day before. As soon as you have ovulated the collapsed follicle starts producing another hormone called progesterone.For illustration purposes only
Preparing for the next period...
As the corpus luteum (empty follicle) shrinks and if the egg is not fertilised, levels of estrogen and progesterone decrease. Without the high levels of hormones to help maintain it, the thick endometrial lining starts to break down, and your body sheds the lining. This is the start of your period and the beginning of your next menstrual cycle.
As the empty follicle shrinks, if the fertilised egg has not implanted into the womb, your level of progesterone decreases. The womb no longer needs to maintain an environment to support a baby so your body needs to reset ready for the next cycle. Any PMT (Pre-Menstrual Tension) symptoms that you have will start to decrease. Without the high levels of hormones to help maintain it, the thick womb lining which has built up starts to breakdown and your body will shed this. This is the start of your period and the beginning of your next cycle. For illustration purposes only
If the egg has been fertilised and implanted into the womb, the empty follicle is maintained by the increasing level of pregnancy hormone [human Chorionic Gonadotrophin]. It continues to produce estrogen and progesterone for much longer until the placenta is mature enough to support the developing embryo. For illustration purposes only
If the egg has been fertilised, it may successfully implant itself into the endometrial lining. This usually takes place about a week after fertilisation.
As soon as the fertilised egg has implanted, your body starts producing the pregnancy hormone, human Chorionic Gonadotrophin (hCG), which will keep the corpus luteum active. It continues to produce the hormones estrogen and progesterone to prevent the endometrium from being shed and support the ongoing pregnancy, until the placenta (which contains all the nutrients the embryo needs) is mature enough to maintain the pregnancy.
Hormones and the Menstrual Cycle
Watch our video to discover more about Hormones and the Menstrual Cycle.
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