The Menstrual Cycle Explained

Knowing your menstrual cycle is a great way to get to know your body, whether you consider yourself well-informed, or are just starting out on a journey to better understand your cycle. Read ‘What is the Menstrual Cycle?’ to discover the different phases, the hormones involved and how tracking your cycle can help you plan or prevent a pregnancy.

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How does the menstrual cycle work?

The menstrual cycle (or uterine cycle) is essential for reproduction, but it also plays a role in the wider landscape of our health. The menstrual cycle works with a fine balance of hormones that are released at key points in order to stimulate phases in the cycle. The uterine cycle is the reason we get periods and why we experience various symptoms such as menstrual cramps. There’s much more to the menstrual cycle than menstruation, it’s just the (very important) tip of the iceberg.

How long is the menstrual cycle?

The length of menstrual cycles varies. However, regular cycles are thought to be between 21 and 35 days in length. While 28 days has often been considered the average cycle length, our latest research into the menstrual cycle revealed that only one in eight women experience a 28-day cycle. It’s also worth keeping in mind that some women are very regular and other women may find their cycles frequently change. There are also medical conditions such as PCOS and thyroid conditions which can cause fluctuation in cycle lengths and you should speak to a healthcare professional if you think you may be affected, or have concerns about these.

The menstrual cycle phases

If we break the menstrual cycle down further, it is actually composed of two phases: the follicular phase and the luteal phase. These distinct menstrual cycle phases are unique in their roles. However, both play pivotal parts in the cycle as a whole, and their cyclical nature means that each is essential to the other. It’s a fine balance of hormones and biological triggers that keeps the cycle going.

What is the follicular phase?

The first part of the menstrual cycle, the follicular phase begins on the first day of your period and ends with ovulation, this is approximately 16 days long,  but as all our cycles vary, so does the follicular phase. Hormones are released in this phase which triggers the growth of follicles in the ovaries. There is also a surge in the main female sex hormone, estrogen. A rise in this hormone stops the production of follicles, allowing them to mature. One follicle eventually becomes dominant and releases an egg cell.

Your basal body temperature is lower during the follicular phase. There is also an increase in luteinizing hormone right before ovulation. This can also be detected with an LH urine test which can help confirm where you are in your cycle.

What is the luteal phase?

The second stage of the menstrual cycle is called the luteal phase and takes place after ovulation and before your period. The dominant follicle, or corpus luteam, produces progesterone, which is a hormone that causes body temperature to rise. It’s this progesterone which also causes the uterus lining to soften and prepare to shed.

If the egg is not fertilized, the uterus lining sheds, leading to your period. It’s during the second phase of the menstrual cycle in the days leading up to your period that PMS symptoms can occur.

The link between hormones and temperature

During the menstrual cycle, body temperature rises and falls slightly due to the change in hormone levels. The shift in temperature is slight, yet significant. It requires a basal body thermometer to detect – that’s a thermometer that shows two decimal places. By measuring body temperature most mornings, it’s possible to identify ovulation, and with this information, it’s also possible to narrow down the fertile window and use this info to either prevent or plan a pregnancy.

Menstrual cycle tracking

Tracking your menstrual cycle and finding ovulation has many benefits. By knowing where you are in your unique cycle you’ll be able to predict your period and plan ahead for PMS and period cramps. Natural Cycles goes one step further. Our intelligent birth control app is used in combination with a basal body thermometer, so you can track your cycle and know your daily fertility. If you’re looking for a hormone-free birth control method that can teach you about your unique menstrual cycle, find out if Natural Cycles could work for you. 

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Written By

Jennifer Gray

A writer with a passion for women’s health, Jennifer Gray has years of experience writing about various reproductive health topics including birth control, planning pregnancy, women’s anatomy, and so much more.

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Scientifically Reviewed

Jack Pearson

With 10 years of experience working in the field of fertility, Dr. Jack Pearson is Natural Cycles’ in-house expert. As Medical Affairs Manager, he dedicates his time to conducting groundbreaking research and educating healthcare professionals.

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