Everywhere I look, I see articles about the “Four Phases of the Menstrual Cycle,” and it drives me and every other OB-GYN absolutely insane.
But what is the scientific truth to this dubious claim? Let’s get to the bottom of the statement to see where the confusion comes from and what the real phases of the menstrual cycle are.
The “four phases” of the menstrual cycle are as follows:
2. Follicular phase
3. Ovulatory phase
4. Luteal phase
This claim mixes up the two organ cycles of the menstrual cycle and tries to combine them into one, which is not how it works.
Repeat after me: There are not four phases of the menstrual cycle!
Your menstrual cycle is actually a bit more complex than this — and in my opinion, it is far more interesting.
There are actually two different organ cycles that contribute to your full menstrual cycle: the ovarian cycle and the uterine/endometrial cycle.
And each of these cycles has three phases. The ovarian cycle has the follicular phase, ovulation and the luteal phase, while the uterine/endometrial cycle has menses, the proliferative phase and the secretory phase.
Let’s break down each phase and how they correspond to each other.
The follicular phase of the ovarian cycle is when the brain sends the ovary signals to tell it to recruit a follicle to get ready to ovulate. This phase lasts approximately 14 days but can be shorter or longer depending on the individual.
Simultaneously, while the ovary is in the first half of its follicular phase, the endometrium is shedding its lining, which is your period. As the ovarian follicular phase continues to grow a follicle to ovulate from, the follicle is sending out more and more estrogen. As this estrogen from the ovary increases, it is also telling the endometrium of the uterus to enter the proliferative phase. This is when the lining of the endometrium starts to thicken to potentially get ready for future implantation of a fertilized egg, resulting in a pregnancy.
I know this is clear as mud, but to sum up the first half of the menstrual cycle: the ovarian follicular phase directs the uterine endometrium through menses and its proliferative phase.
Now, we’re halfway through the menstrual cycle. The ovary has completed its first phase (the follicular phase) and is ready to ovulate. The uterus has completed both the first phase of menses and the second proliferative phase to thicken its lining.
Ovulation is then triggered and completed in the ovary, and the ovary enters its third phase, called the luteal phase.
The luteal phase of the ovary is when the leftover ovarian follicle starts secreting progesterone. This progesterone from the ovary tells the uterine endometrium to enter its last phase, called the secretory phase.
During the secretory phase of the endometrium, the progesterone from the ovarian luteal phase stabilizes the endometrial lining to help support a potentially implanted fertilized egg (if an egg was fertilized by sperm during ovulation).
So, the ovarian luteal phase corresponds to the endometrial secretory phase.
If a fertilized egg does not implant or the egg was never fertilized by sperm, both the ovarian and endometrial cycles end and start all over again with the ovarian follicular phase and the endometrial menses phase.
Not confusing at all, right???
Don’t worry — it takes us doctors four years of medical school and four years of OB-GYN residency to fully understand the intricacies of the menstrual cycle. If you need to, feel free to watch this video a couple more times to more fully understand!
I can see why people tried to simplify it down to four phases, but technically, menses is part of the endometrial cycle, not the ovarian cycle, and it occurs during the follicular phase of the ovarian cycle.
Understanding our bodies is essential for optimizing how our bodies work for us — how we can improve our menstrual cycles, prevent or plan for pregnancy, and also understand why we feel the way we do.
If we truly want to understand our bodies, let’s get it right!
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