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09/5/18

Your menstrual cycle explained

By Dr Vanessa Pataia, PhD



How well do you think you know what exactly happens during you cycle? Not that well? In that case read on, this blog post is for you!
Most women know that their period comes from the breaking down and shedding of their uterine lining, if they didn’t get pregnant that month. However, most women don’t know exactly how or why it happens. This is in part because periods have been a taboo in our society for so long. Given that they are something that will happen to half of the world’s population at some point in their life, it is time to break the taboo, don’t you agree?

So what happens during a menstrual cycle?
The menstrual cycle has 4 phases: menstrual phase, follicular phase, ovulation and luteal phase. A full menstrual cycle can last anywhere between 21 – 35 days and its length can change each month depending on things like stress, changes in weight and physical activity or travelling.

When does each cycle start?
Each cycle starts with the menstrual phase, when a period starts. During this phase, the lining of the uterus sheds which can cause cramps in the abdomen, back and upper thighs. Periods can last 2-7 days normally, and the menstrual fluid contains blood, cells from the uterine lining and mucus.
During this phase, your body already starts preparing for your next cycle. Women are born with all their eggs in their ovaries. At puberty there are around 400,000 eggs in a women’s ovaries held inside ‘immature’ ovarian follicles. Each month approximately 3- 30 ovarian follicles start developing and this is called the follicular phase.

How do eggs develop for ovulation?
During the follicular phase, a hormone called follicle stimulating hormone (FSH) is produced by the brain. This hormone stimulates the growth of the ovarian follicles so that the eggs inside can maturate and be ovulated. As the ovarian follicles grow, they compete for FSH until eventually one follicle becomes ‘dominant’ while the remaining follicles die. The growth of the follicles also stimulates the production of oestrogen by the ovaries. Oestrogen stimulates the thickening of the uterine lining in preparation for a pregnancy. Oestrogen levels continually rise and reach their peak before ovulation. During this phase you may feel in a better mood and have more energy.

What causes the ovulation of an egg?
With the rise in oestrogen levels, the brain starts producing a hormone called luteinising hormone (LH). LH triggers the ovulation of the egg inside the dominant follicle by causing the ovarian follicle to rupture and allow the egg to be picked up by one of the fallopian tubes. If while traveling down the fallopian tube, the egg meets a sperm it can be fertilised and become an embryo. The fertilisation window for an egg is 12-24h after being released but because sperm can survive inside a women’s reproductive tract for up to 7 days, it is important to use protection during the days leading up to ovulation if you want to prevent a pregnancy.

What happens after ovulation?
The last step of the menstrual cycle is called the luteal phase and lasts around 11 to 14 days. After the release of the egg into the fallopian tube, the follicle that held it becomes a corpus luteum. The corpus luteum produces oestrogen and a new hormone, progesterone. The progesterone makes sure that your uterus keeps building up its lining in preparation to receive an embryo. But if the egg has not been fertilised, the oestrogen and progesterone levels drop and the uterine lining starts to break down and shed, initiating a new cycle. A few days before your period you may experience some Premenstrual Syndrome (PMS) symptoms and this is because of the drop in oestrogen and progesterone levels that anticipate the breaking down of the uterine lining.

So do you feel like you’ve learned one thing or two about your body? Then keep an eye on our blog, our next blog post will be about reasons for spotting in between periods!

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