Menstrual Cycle Basics

Understanding menstrual cycle basics

Understanding menstrual cycle basics may help you understand why you feel how you feel. Notice in the menstrual cycle chart below when estrogen and progesterone levels are low, when they are high, and when they are changing during your cycle.

Low hormone levels occur at the beginning and end of the menstrual cycle.

Changing hormone levels — note the days on which the slope of the lines is steepest. For many women, symptoms arise when levels are changing. For example, menstrual migraines often occur right before the period when estrogen levels are dropping.

TRACKING YOUR CYCLE

How do you feel during the different parts of your cycle? If you are tracking your menstrual cycle this will be easier to figure out.

Tracking Your Cycle

A menstrual cycle hormone chart

There are three parts to a menstrual cycle:

FOLLICULAR PHASE

Menstrual flow/bleeding (lasts from 1-7 days)
Low levels of estrogen and progesterone from the end of our last cycle cause follicle-stimulating hormone (FSH) to rise
FSH stimulates egg (follicle) development. A follicle is a cavity in the ovary containing a maturing ovum (egg) surrounded by its encasing cells. An average of 3-30 follicles mature per cycle
Developing eggs (follicles) produce estrogen, resulting in an estrogen surge
Estrogen causes growth of the endometrial lining

OVULATION

Estrogen surge causes luteinizing hormone (LH) to peak, which triggers ovulation
One “dominant” follicle (egg) bursts from the ovary
The remaining developed follicles die (called “atresia”)
The area on the ovary from which egg (follicle) appears is called the corpus luteum
Corpus luteum produces progesterone (and estrogen for the second half of a cycle)

LUTEAL PHASE

Progesterone enriches the endometrium to prepare for a fertilized egg
If no egg is fertilized, progesterone levels fall and endometrial lining is shed during flow
Next cycle begins

Note: In the chart above, we have put estrogen and progesterone on the same scale (y-axis) as most sources do. In reality, estrogen rises 220% above its day 1 level during a cycle, while progesterone rises 1,400%. This is not a typo! Estrogen levels are most often measured in picograms/milliliter, and progesterone in nanograms/milliliter (1 picogram = .001 nanograms).

Learn more about menstrual cycle basics

From our founders:

WLB Founder’s Personal Story about Menstrual Cycle Changes

The “Learn More, Feel Better” series:

Can You Picture Your Cycle? (i.e. how our menstrual cycles work)
What Changes, When, and Why? (i.e. how our cycles change as we enter the many-year menopause transition)
This Isn’t Me! (i.e. why some of us feel “so not like ourselves” )