Understanding the Menstrual Cycle: Phases and Hormones Explained

The human body continuously goes through cycles all the time. And here at Mira, one of our favorite cycles is… the menstrual cycle! 

In this article, we’ll cover everything you need to know about the stages of the menstrual cycle – including what happens during each stage, how hormones drive key processes, and what this means for your fertility and hormone health. 

The Menstrual Cycle Stages Explained

Menstruation

The first phase of the menstrual cycle is the follicular phase, which begins with menstruation (i.e. your period). 

Over the course of the menstrual cycle, the lining of the uterus builds up and ‘thickens’. It does this in preparation for pregnancy. However, if conception does not occur, the uterine lining sheds and passes through the vagina. This is what you see as your period, and it is made up of tissue, blood, and cells from the uterine lining. 

On average, periods last around 2 to 7 days. It’s good to keep track of your period so that you know when your cycle starts and how long it lasts. This information is helpful for planning a pregnancy, avoiding pregnancy, and monitoring your reproductive health.

Alongside menstrual bleeding, it’s also common to experience breast tenderness, cramping, muscle aches, headaches, fatigue, lower back pain, and bloating during your period. 

The Follicular Phase

The follicular phase technically starts on the first day of your period. It lasts around 14 days, with the start of menstruation marking the beginning of the follicular phase and ovulation marking the end of the follicular phase. 

Early in the follicular phase, gonadotropin-releasing hormone (GnRH) triggers the pituitary gland to release follicle-stimulating hormone (FSH), which stimulates the growth of several egg follicles in the ovaries. Over time, a dominant follicle develops and becomes an egg ready to be fertilized. This dominant follicle releases estrogen, which helps to thicken the lining of the uterus in preparation for implantation. 

At the start of the follicular phase, it’s normal to experience symptoms related to your period. Once your period has finished, these symptoms will likely subside and leave you feeling more energized.  

Ovulation

When estrogen peaks, this tells the brain that an egg is ready to be released from the follicle. The brain then releases a surge of luteinizing hormone (LH), which informs the ovarian follicle to release the egg into the fallopian tube. This process is called ‘ovulation’. The empty follicle left behind becomes the ‘corpus luteum’, which goes on to produce progesterone to support a potential pregnancy. 

In terms of timing, ovulation often occurs around 24 to 36 hours after the surge in LH. For 28-day cycles, this is around cycle day 14.

Ovulation is absolutely critical to fertility, as natural conception is only possible if ovulation occurs. Sperm can survive inside the reproductive tract for up to five days, and you are considered at ‘peak’ fertility during the five days leading up to ovulation, the day of ovulation, and one day after ovulation. After the egg is released, it has only up to 24 hours of life span to be fertilized by a sperm. 

Common symptoms of ovulation include light cramping, ovulation bleeding, breast tenderness, and increased libido. Basal body temperature (BBT) also slightly increases just after ovulation. This slight increase can be detected with a BBT thermometer to confirm ovulation occurred. 

The Luteal Phase

After the egg is released through ovulation, this marks the start of the luteal phase of the menstrual cycle. During this time, the body is busy preparing for implantation and a possible pregnancy. The corpus luteum produces progesterone, which helps to thicken the uterine lining and prepare the uterus for implantation. 

If you are pregnant, the corpus luteum will continue to make progesterone to help sustain your pregnancy. If the egg is not fertilized, the corpus luteum will shrink, and it will no longer produce progesterone. Eventually, the uterine lining sheds – marking the start of your next period and the cycle repeats. 

In a 28-day cycle, the luteal phase lasts around 14 days. However, timings can vary greatly among individuals. 

Rising progesterone levels can lead to a number of luteal phase symptoms including fatigue, mood changes, breast tenderness, bloating, and acne. 

Key Hormones Involved in the Menstrual Cycle

Estrogen: The Growth Hormone

When a dominant follicle begins to develop during the follicular phase, it starts to produce estradiol (E2). Estradiol is the dominant form of estrogen that helps to regulate the menstrual cycle in individuals of reproductive age. 

Estradiol often starts to rise about 4 to 5 days before ovulation, reaching its peak approximately a day before ovulation. After ovulation, estradiol levels drop. Midway through the luteal phase, estradiol levels rise slightly before dropping off again right before your period. During this time, estradiol works to thicken the uterine lining to prepare for implantation. 

When estradiol levels are elevated right before ovulation, you may feel more energized than normal. You may also notice positive changes to your skin, mood, and libido. This is nature’s way of letting you know you’re fertile. 

Tracking when estradiol levels rise can be helpful for estimating your fertile window and predicting ovulation. This can be done with the Mira Monitor, which can measure E3G (the urinary metabolite of estradiol). 

Progesterone: The Pregnancy Hormone

Progesterone levels ramp up during ovulation and remain elevated throughout the majority of the luteal phase. The role of progesterone during this time is to help prepare the uterine lining for implantation and stabilize the implantation process by preventing muscle contractions. 

If pregnancy does not occur, progesterone levels drop and your period begins. This drop in progesterone is often the culprit behind the typical luteal phase symptoms – such as fatigue, breast tenderness, and bloating. 

Tracking exactly when progesterone rises and when it remains elevated can be helpful for confirming ovulation. This can be done with the Mira Monitor and Mira’s Confirm Wands, which can measure PdG (the urine metabolite of progesterone).   

Follicle-stimulating Hormone (FSH)

At the start of the menstrual cycle during the follicular phase, the pituitary gland releases FSH. The primary role of FSH is to help stimulate the development of premature ovarian follicles. Eventually, a dominant follicle will develop and be released as an egg through ovulation. Without FSH, this process would not be possible. 

In addition to follicular development, FSH also helps to boost estrogen (estradiol) levels ahead of ovulation. This increase in estrogen helps to thicken the uterine lining in preparation for implantation.  

FSH levels are typically highest during the follicular phase, reaching their peak during ovulation. After ovulation, FSH levels drop before rising slightly just before your period in preparation for the next follicular phase. 

Keeping track of your FSH levels can provide insights into your ovarian functioning and general reproductive health. For example, if FSH levels are too high, this may be a sign you’re approaching menopause. If FSH levels are too low, this may indicate an underlying health condition such as hypopituitarism or polycystic ovary syndrome (PCOS). 

Monitoring your FSH levels at home is possible with the Mira Monitor and Mira Ovum Wands, which can measure numeric FSH levels in urine. 

Luteinizing Hormone (LH)

During the follicular phase, LH stimulates developing ovarian follicles – helping to produce estrogen. Then, approximately 24 to 36 hours before ovulation, the brain ramps up production of LH. This rapid rise in LH is known as the LH surge, and it is what triggers the release of an egg from the ovaries. After ovulation, LH levels rapidly decline back to their baseline level. During this time, LH stimulates the corpus luteum – helping to produce progesterone during the luteal phase. 

The importance of LH cannot be stressed enough, as it plays a critical role in stimulating both estrogen and progesterone production while also triggering the process of ovulation. 

If you are actively TTC, being able to identify and track your LH surge is helpful for getting pregnant efficiently. Once you’ve identified elevated LH levels, this means you’re about to ovulate and reach peak fertility for the current cycle. You can then plan sex with your partner accordingly when your chances of conception are highest. 

Many people use traditional ovulation predictor kits (OPKs) to identify their LH surge. However, OPKs do not always work for every cycle. A more accurate way to identify your LH surge is by measuring your LH levels directly with the Mira App and Monitor, which can measure numeric LH levels in urine.  

Staying In Tune With Your Hormone Health: Why You Should Check Your Hormones

Hormones affect nearly every aspect of our lives – from our mood, appetite, and energy levels to our ability to start a family. By staying in tune with what your hormones are doing, you can make informed decisions for your reproductive health.  

For daily hormone monitoring, the Mira Hormone Monitor can help you track up to four key fertility hormones in urine – including E3G (the urinary metabolite of estradiol), PdG (the urinary metabolite of progesterone), FSH, and LH. Your numeric results are then tracked in real-time in the Mira App, enabling you to see your unique hormone patterns over time. This detailed information is helpful for planning a pregnancy or managing hormone imbalance. 

For a ‘big picture’ perspective of your overall reproductive health, you can also utilize Mira’s Panorama Fertility Lab Test. This one-time blood test can provide insights into other hormones that affect the menstrual cycle – including Anti-Müllerian hormone (AMH), thyroid-stimulating hormone (TSH), Free Thyroxine (fT4), Prolactin, and Free Testosterone. Once your hormones are tested, you’ll receive five detailed reports that provide insights into your menstrual cycle rhythm, ovarian reserve, hormone balance, and more. 

*Please note that Mira’s Panorama Fertility Lab Test is not the same as the Mira Monitor. The Panorama Fertility Lab Test is a one-time screening that provides a broad picture of overall reproductive health and ovarian reserve. The Mira Monitor is designed for ongoing use to help monitor hormonal trends related to fertility and ovulation. 

Signs of Hormone Imbalance

The most common signs of hormone imbalance include:

• Difficulty getting pregnant
• Heavy menstrual bleeding
• Irregular or missed periods
• Acne and/or oily skin
• Hair loss or thinning on the head
• Excessive hair growth on the face, arms, back, chest, or abdomen
• Unexpected weight gain

If you suspect your hormones are out of balance, it’s worth having your hormones tested with Mira’s Panorama Fertility Lab Test. This test provides you with five detailed reports – including a Fertility Health Report, Ovarian Reserve Report, Hormonal Balance Report, Thyroid Function Report, and Menstrual Cycle Rhythm Report. These reports can help you better understand your symptoms and fertility. You’ll also get an indication of whether or not you should speak with your doctor about your hormone health. 

When to Seek Support

If you are actively trying to conceive (TTC), it’s recommended to seek help from a doctor if you have been trying to get pregnant for at least 12 months (if under the age of 35) or at least six months (if over the age of 35) without success. 

If you’re not necessarily TTC but experiencing symptoms of hormone imbalance that are new, persistent, or interfere with your day-to-day life, seek help from a doctor. 

We know that navigating your hormones and fertility can feel isolating, but there are a lot of things you can do from home to manage your hormone health in between appointments. 

For example, you can keep track of your cycle and symptoms with a cycle-tracking app (such as the free Mira App). You can also monitor your hormones directly with the Mira Monitor – or, consider trying to make a few lifestyle changes that can help balance your hormones naturally. 

For extra support, you can also speak with a certified fertility coach at Mira’s own Hormone Health Clinic for Fertility. 

Final Thoughts

No matter what your fertility goals are, we want you to feel empowered to take control of your hormones and reproductive health.

To learn more about your hormones, check out Mira’s Sex Hormones Awareness Week. You may also find our library of free webinars, ebooks, and blogs helpful for planning a pregnancy or navigating your hormone health. 

Frequently Asked Questions