Written by Dr. Seif Sadek

Many people think that the hormone cycle is something that only involves your uterus and ovaries, but it’s actually a well-orchestrated cycle of hormones and signals between lots of different organs in your body. Your brain and reproductive system work together so that your body can release an egg for a potential baby 👶 in a process known as fertilization. This usually happens every month or so and is split into two phases: the follicular and the luteal phase (more on the two phases below ⏬). 

So, what do we mean by a cycle of “hormones”? Hormones are messengers that send messages to various parts of the body, some of which contribute to the regularity of your cycle. Here are a few key players:

Those produced by the brain 🧠: 

1. Luteinizing hormone (LH): Initiates ovulation, a small window each month when the egg is ready for fertilization
2. Follicle stimulating hormone (FSH): Stimulates the growth of eggs in the ovaries

Those produced by the ovary 🥚:

1. Estrogen: Dominant in the first half of your cycle and allows the eggs in your ovaries to grow
2. Progesterone: Dominant in the second half of your cycle and key in maintaining the inner lining of your uterus in preparation for pregnancy

Note: period ≠ cycle

Your period 🩸 is the 2-7 days when you’re actually bleeding, while your cycle is counted from the first day of bleeding of one period to the first day of bleeding of the next period. That means that your period is only a small part of your 21-35 day cycle. A lot of things are happening within your body in between periods, which we’ll break down next.  

The first half (aka the follicular phase) 

The follicular phase is known as the egg growing phase that lasts 9-14 days. During the first half, estrogen is the dominant hormone. It allows the eggs to grow and eventually select a dominant one. Once that dominant egg has reached peak size, it signals the brain to release LH, initiating ovulation. We call this the “LH surge”, and it allows the ovary to release the egg into the fallopian tube in preparation for a potential pregnancy 🤰.

Follicular phase of the menstrual cycle

The second half (aka the luteal phase)

The release of the egg marks the beginning of the second half of the cycle, or the luteal phase, initiating the production of the second ovarian hormone, progesterone, and lasting exactly 14 days. This hormone is key in maintaining the inner lining of your uterus in preparation for pregnancy. Fun fact: the word “luteal” is derived from the Latin word yellow, because of the appearance of the ovary during this time! 

Luteal phase of the menstrual cycle

After those 14 days, both the estrogen and progesterone production drops significantly, allowing the uterus to shed the lining for the start of a new menstrual cycle. This also allows FSH to signal the ovaries to start growing new eggs. 

What’s considered a “normal” cycle?

What’s “normal” for me may not be “normal” for you. Your cycle can be regular and about the same length every month while your friend may have a little bit more variation in how long their cycle is. Your periods may be heavy and long, and your friend’s might be light and short. Within a broad range, "normal" is what's normal for you.

However, there can also be a multitude of reasons why your menstrual cycle is irregular:

Pregnancy 🤰

Pregnancy is the most common reason. Skipping a period can be the first sign you are pregnant and is usually the first thing you should check if you’re experiencing cycle irregularities. 

Imbalance in your hormones produced by the brain 🧠 or the ovaries 🥚

A common example that can affect the hormones produced by the brain is extreme weight loss and/or exercise, commonly referred to as the “female athlete triad”. When you lose a ton of weight at once, your body produces drastically less leptin (a hormone that helps the body maintain weight). Remember that your brain is the conductor of an orchestra of hormones, so one hormone production can affect another

Imbalances in estrogen or progesterone production 

The most common disorder is Polycystic Ovary Syndrome (PCOS), where people have higher levels of estrogen and low levels of progesterone. PCOS can also cause elevated LH, which can also lead to irregular periods. 

Structural changes in the muscle of the uterus or the lining

The most common structural cause of menstrual cycle changes are uterine fibroids, which are noncancerous muscular growths of the uterus that can cause heavy and prolonged periods (read more about the different disorders in our blog on period pain 👉here👈). Approximately 70% of people with periods will have fibroids in their lifetime, but only 1% will see a doctor due to fibroids. 

Ultimately, visit your doctor about your cycle if: 

• You have gone more than 90 days without a period and you’re not pregnant
• You are experiencing heavy periods that soak through two pads or tampons in one hour 
• You develop severe pain with your period
• Your periods have been previously regular and suddenly become irregular
• Your period lasts more than 7 days
• You have any concerns regarding your period

What you can do 

All people with cycles should keep track of their cycles to spot out any irregularities. One simple way is to download our free Aavia app ✌️ Our app can help you notice patterns in your cycle and analyze what factors are leading to your cycle changes. Plus, it’ll help your doctor ID your cycle patterns and provide better diagnoses for you!