We talk about it a lot, but have you ever wondered, wait…what IS a menstrual cycle? Everyone with a uterus (and even those without) should understand this important body process and why we experience it in the first place. Essentially, the menstrual cycle is the term used to describe the hormonal and physical changes that occur in a repeated pattern from the first day of a period to the day before the next period. It’s a short amount of time, but a lot happens during every cycle. Let’s break it down.
The four phases
The menstrual cycle can be divided into four main phases: menstruation, the follicular phase, ovulation and the luteal phase. Each phase has unique characteristics.
- Menstruation: Menstruation (or ‘a period’) describes the loss of blood and tissue from the vagina. On the inside, the uterus is shedding its lining, and small blood vessels are breaking open in the process. Day one of menstruation is considered the start of the menstrual cycle. It usually lasts three to seven days.
- Follicular Phase: The first part of the follicular phase includes menstruation, and it continues up until ovulation. During this time the brain is sending increasing levels of hormones (specifically follicle-stimulating hormone and luteinizing hormone) to the ovaries to prepare a few eggs for release. The eggs develop in something called a follicle, hence the term ‘follicular phase.’
- Ovulation: Ovulation happens in the middle of the cycle (or 14 days before the next period, to be more precise). It’s the term for the release of an egg from one of the ovaries. Once released, the egg travels down the fallopian tube toward the uterus. If present, this is where a sperm may fertilize (or fuse with) an egg. If no sperm are present, the egg will either disintegrate or pass from the vagina after 12-24 hours. Importantly, the days leading up to and including ovulation are the time during which risk of pregnancy is the highest.
- Luteal Phase: Once ovulation occurs (and the egg has passed from the vagina unfertilized), the luteal phase begins. The uterine lining builds up as progesterone increases, then slowly starts to break down as progesterone decreases. This phase is around 14 days for most people and continues right until the day before the next period.
The process repeats itself in a very predictable pattern, defining what a menstrual cycle is.
What are menses?
‘Menses’ is another term for menstruation (or a number of other nicknames). The average age for the start of menses is between 11 and 12 years old, though both environment and genetics play a significant role in when someone gets their first period.
During the first two to three years, menses can be unpredictable as your hormones get settled into a rhythm, but your cycle should ultimately fall into place. The average cycle length can be anywhere between 25 and 38 days and remains consistent from month to month. Besides heavy vaginal bleeding, other common complaints about menses include cramps (spreading from the lower pelvis to the thighs, even to the back and to the rectum), headaches, acne, bloating and fatigue. Cramps can range from mild aches to incredibly painful and debilitating.
When cramps are caused by your period, they are called ‘primary dysmenorrhea.’ When cramps are caused by a condition other than your period, they are called ‘secondary dysmenorrhea.’ There are many treatments for dysmenorrhea. Things you can do at home include heating pads, getting regular exercise, rest and using over-the-counter medicines. Whenever the pain interferes with daily activities, or if it gets worse over time, It’s worth talking to your primary care physician or gynecologist.
Why things happen on a cycle
The menstrual cycle is one example of the many ways our bodies operate on autopilot. In this case, hormones released from the brain send signals to the ovaries to prepare for ovulation. The hormones released after ovulation rise and fall, causing a period, which sends signals back to the brain to start the cycle all over again. There are quite a few more details, but the way hormones work is the reason why our periods run on a cycle. It’s a continuous feedback loop.
The menstrual cycle from start to finish is measured from day one of a period to the day before the next period. It usually lasts about 28 days, though a cycle between 23 and 38 days can be normal. The main reason why a cycle may temporarily be disrupted is pregnancy, but a number of other factors can influence the pattern of a menstrual cycle.
Why your cycle might be irregular
There are a number of reasons why a cycle can be irregular. The majority of the time these causes are temporary and correct themselves. Here are some of the main reasons why a cycle might not be regular:
- Stress: Stress causes an increase in cortisol levels which can impact the hormones involved in the menstrual cycle. Stress comes in a variety of forms including illness, personal struggles or professional problems. If you experience a significant life event it is possible that your period will be impacted.
- Diet: It takes a lot of energy to have a period every month. If you lose a lot of weight quickly, or if your body does not have enough energy stored up, the menstrual cycle may be impacted.
- Exercise: In a similar manner, if you exercise excessively, you may burn off too much energy for your body to keep up. If there is not enough energy in your body, periods can become irregular.
- Where you are in your cycle: It is very common for periods to be irregular for the first few years after they start. Irregularity is also common for many years leading up to menopause.
- Medications: With an understanding of what a menstrual cycle is, it makes sense that some medications (like birth control pills and emergency contraception) can disrupt hormone signaling and cause cycle changes. These changes are reversible once the medication is out of your bloodstream.
- Other health conditions: There are a number of health conditions such as polycystic ovary syndrome (PCOS) or thyroid abnormalities that are known to impact the menstrual cycle. If you begin to notice abnormalities in an otherwise predictable cycle, it’s worth talking with a doctor.
What to do if your cycle isn't regular
In order to know whether your cycle is regular or not, you first need to track your menstrual cycle. There are a variety of apps and online tutorials that can help. If your cycle is not around the same number of days from month to month, consider discussing it with your doctor. From there, they may check labs or discuss medications you can take to help regulate your cycle. Many medications that restore cycle regularity, like birth control pills, are also treatments for dysmenorrhea (period cramps).
Conclusion
To bring this full circle, there is tremendous benefit in understanding what a menstrual cycle is. It can help you plan and pack for your next period, avoid a mistimed pregnancy or increase the chance of conceiving. An understanding of a menstrual cycle can also allow you to predict period symptoms and plan for optimal relief. And whenever in doubt, you can always discuss with your doctor.