Menstrual Cycle Phases and Hormones

Most women who have entered their reproductive years experience a menstrual cycle. The menstrual cycle is the body’s way of preparing for pregnancy. The only times a woman won’t have a regular menstrual cycle (referred to as amenorrhea) is when pregnancy occurs, breastfeeding, or after menopause.

The menstrual cycle consists of 4 main stages and each stage is caused by the release of certain hormones. Hormones are chemical messengers found in the body and are responsible for the transition from one menstrual phase to the next. 

Depending on which hormones are present is directly related to how you feel mentally, emotionally, and physically at any given time of the month. 

How Hormones Affect You During Your Menstrual Cycle 

Your normal menstrual cycle can be divided into 4 important phases, each governed by a different cocktail of hormones. If your menstrual cycle was a 4-part symphony, your hormones would be the musicians; they control the mood and tone at any given time of the month.

The average human menstrual cycle is 28 days, and the first day of menstruation (or the menstrual phase) signifies day 1 of your cycle. Having said that, there's normal variation. Many women experience a cycle length as short as 21 days or as long as 35 days during their reproductive life. Moreover, many women experience irregular menstrual cycles, which can be caused by many factors. 

Do not be alarmed if your body doesn’t run like steady clockwork month to month. There is a normal range in the four phases, and there will be differences in when your cycle starts. What's considered a "normal menstrual cycle" can vary.

Let’s dive deeper into each of the 4 main phases of the menses cycle, the role of hormones, and how they might make you feel during each particular phase.

Menstrual Phase

During menstruation, your female sex hormone levels (estrogen and progesterone) take a nosedive. This radical drop in hormone levels causes the collapse of your uterine lining. During menstrual bleeding, your uterus then sheds its lining (endometrium) along with the unfertilized egg through the vagina. 

The first day of a menstrual period represents day 1 of your cycle and typically lasts about 5–7 days. It’s more commonly referred to as your period.

Signs & Symptoms of the Menstrual Phase

As a result of the sudden drop in female sex hormones, the menstrual phase is often the phase when you’ll experience the most dramatic symptoms. During your menstrual phase, you may experience all or none of the following:

• Abdominal cramps
• Tender breasts
• Bloating or fluid retention
• Lower back pain
• Headaches
• Acne 
• Diarrhea or constipation
• Low energy, fatigue
• Cravings for specific foods
• Mood swings
• Trouble sleeping

Follicular Phase

The follicular phase of your cycle includes menstruation and extends to the ovulation phase, at around day 14.

The Role of Follicle Stimulating Hormone

When the follicular phase begins, your pituitary gland releases follicle stimulating hormone (FSH). 

Follicle stimulating hormone does exactly as its name implies—stimulates follicle growth on the ovaries. About 5–20 tiny follicles collect on the ovary’s surface, each containing an oocyte (immature egg). Only one of those eggs will mature and be released when you ovulate.

The follicles trigger a surge of estrogen and progesterone levels that stimulates the uterine lining to thicken in preparation for a possible pregnancy.

How You Might Feel During the Follicular Phase

You’re in luck! Aside from the menstrual phase (day 1–7), the changes occurring in your body during the rest of the follicular phase (day 8–13) are typically not observed. 

Ovulation

Ovulation is the phase of the menstrual cycle when you’re most fertile—and you have luteinizing hormone (LH) to thank for that! 

Luteinizing hormone is released by the brain’s pituitary gland in the days leading up to ovulation. The surge of luteinizing hormone released by the pituitary gland causes one of the ovarian follicles to burst from the ovary, travel down the fallopian tube, and become an ovum (or egg).

The egg stays there for about 24 hours waiting for a single sperm to fertilize it. At that point, the egg either gets fertilized by a sperm or it doesn’t. 

If the egg is not fertilized, pregnancy won’t occur and the corpus luteum withers and dies as the body prepares to shed its uterine lining and start the menstrual cycle over again. This typically occurs around day 22 of a 28-day menstrual cycle. 

Signs & Symptoms of the Ovulation Phase

The symptoms of ovulation are primarily physical, rather than emotional. Women often use devices to detect these changes such as a sensitive thermometer or ovulation predictor kit that measures your levels of LH. 

When ovulation occurs, other changes include: 

• Drop in basal body temperature falls just before ovulation
• Rise in basal body temperature 24 hours after the egg’s release
• Cervical mucus changes indicating when ovulation might occur
• Creamy: Ovulation may be coming
• Wet or watery: Ovulation may start soon
• Wet and stretchy (egg white texture): You may be ovulating
• Your cervix softens and opens up (sometimes known as having a short, high, open, and wet cervix or SHOW) 
• Slight twinge or cramping (a.k.a. mittelschmerz)
• Light spotting (caused by the tiny follicle ruptures when the oocyte, or immature egg, is released)

Luteal Phase

The luteal phase begins approximately 17 days into your menstrual cycle and lasts around 11 days. After the oocyte bursts from its follicle during ovulation, the ruptured follicle stays on the surface of the ovary and slowly transforms into a structure called the corpus luteum.

The corpus luteum releases progesterone (along with small amounts of estrogen). These increased progesterone levels maintain the thickened lining of your uterus, in preparation for the implantation of a fertilized egg. 

There are 2 main things that can happen during this phase, which determine the hormones that are present:

1. The egg is fertilized and implants: If fertilization occurs, the fertilized egg produces a hormone called human chorionic gonadotropin (HCG) hormone. This is the hormone detected during a pregnancy test. The corpus luteum will also continue to produce progesterone to maintain the thickened lining of the uterus (endometrium). 
2. The egg is not fertilized: If the egg isn’t fertilized, the corpus luteum dies. Since the corpus luteum is responsible for releasing progesterone, levels of progesterone drop toward the end of this phase causing the uterine lining to fall away.

Signs & Symptoms of the Luteal Phase

Signs and symptoms of the luteal phase vary depending on whether or not you get pregnant. 

The hormones released during this phase are responsible for the symptoms of premenstrual syndrome (PMS). You will notice that a lot of these symptoms are also symptoms of menstruation, such as:

• Bloating and fluid retention
• Breast tenderness
• Cravings 
• Mood changes
• Headaches
• Trouble sleeping

Causes of Hormone Imbalances in the Menstrual Cycle

While hormone fluctuations are necessary for the 4 phases of the menstrual cycle to occur, there are circumstances that can lead to hormone imbalances that disrupt your monthly cycle. 

Factors that can lead to hormone imbalances include medical conditions, emotional factors, and lifestyle choices.

Under normal circumstances, hormone levels change as a woman gets older, ultimately leading to menopause. Menopause typically occurs after the age of 45 and causes menstrual bleeding to stop. 

Some of the factors that can disrupt your hormone balance can be easily managed and others may require more extreme treatments. Either way, no need to panic as hormone imbalances are a common occurrence and can be easy to get under control. Here are some of the main reasons for hormone imbalances in women:

• Autoimmune conditions: Conditions that affect your immune system, like rheumatoid arthritis, can have a knock-on effect for the menstrual cycle because they alter your levels of estrogen.
• Polycystic ovary syndrome (PCOS): PCOS prevents an egg from developing normally and leads to a hormone imbalance. Women with PCOS may have infrequent or prolonged menstrual periods or excess male hormone (androgen) levels. 
• Birth control & other medications: Hormonal birth control deliberately sets out to interrupt your natural menstrual cycle in order to prevent pregnancy. 
• Perimenopause: This is the final stage before menopause (when periods cease completely) and is usually characterized by an irregular menstrual cycle as periods gradually stop. Menopause is diagnosed when you go 12 months without a period.
• Tumors, cysts, or cancers: Anything that affects the natural functioning of the endocrine glands will cause hormone imbalances that impact your reproductive cycle.
• Diet: For example, phytoestrogens are naturally-occurring plant estrogens found in soy products. Consuming extremely high levels can affect your cycle.
• Primary ovarian insufficiency (POI): POI is also known as premature ovarian failure. It occurs when a woman stops producing eggs naturally before the age of 40 and is different from menopause.

Signs and Symptoms of Hormone Imbalances in Women

Some reasons for hormone imbalance, such as menopause or pregnancy, are completely natural and no need for concern. Unless you’re on the birth control pill, it’s also completely normal if your cycle doesn’t work like clockwork month-to-month.

Watch for These Symptoms

However, if you notice any of the following unusual symptoms on a regular basis, it’s advised to consult with your doctor:

• Heavy menstrual periods with a lot of clotting (especially clots larger than a quarter)
• Irregular or exceptionally light periods
• Spotting between periods accompanied by abdominal pain or cramping
• Pain or a burning sensation when peeing
• Unusual vaginal discharge and/or redness and itchiness
• Hair loss
• Vaginal dryness or pain when you have sex
• Unexplained weight gain
• Hot flashes or night sweats
• Growth of facial hair
• Skin tag formation

Written by Jane Flanagan — Updated on April 5, 2022.

We hope you found this post informative — but remember: we’re not doctors and this post is not medical advice! While all posts are fact-checked and well researched, we always recommend you chat with your doctor about any questions or concerns you might have regarding a medical condition. We’re here to support and educate, but never with the aim of disregarding professional medical advice you’ve been given. Phew, now that that’s out of the way, you can go on living unapologetically free.