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  • Dr. Jillian Smithers

Understanding the Menstrual Cycle

Understanding how the menstrual cycle works is the first step in uncovering and identifying underlying hormonal imbalances. Without knowing how this is supposed to work when everything is functioning optimally, it’s very difficult for us to realize if something may be off.

In all of my consults with patients, I begin with a brief explanation of how the menstrual cycle works, what hormones are involved, and what we should be expecting throughout the month. It’s important to me that you as a woman understand what's going on in your body because it gives you the empowerment to take your health into your own hands and advocate for yourself if you feel like something isn’t right. If you’re a current patient of mine needing a refresher, or you’re nodding along as you’re reading this thinking there may be more that you could learn about this topic, please continue!

When we talk about the menstrual cycle, we are talking about the month-long cycle that occurs, not just your period. The entire cycle is an average of 28 days long, but can be considered “normal” anywhere between 21 and 35 days as long as the interval is regular.

Estrogen and Progesterone: The Two Main Hormones Guiding Our Menstrual Cycles

The two main hormones that guide and regulate our menstrual cycles are estrogen and progesterone. These hormones fluctuate greatly throughout each phase of the cycle and play very different, but complementary, roles. Estrogen is what creates the physical changes that we see around our very first period - the development of breasts and rounding out of the hips. It also helps with collagen production in the skin, which keeps our skin plump and hydrated. This is why women can notice skin thinning on the face and body after menopause when estrogen levels dramatically decline. It is also responsible for thickening the inner uterine lining to prepare for implantation of a fertilized egg. Estrogen is mainly produced by the ovaries and secondarily in much smaller amounts from the adrenal glands and fat tissue.

Progesterone, on the other hand, balances out or counters the effects of estrogen. It is our calming, anti-anxiety hormone that increases sleepiness and prepares the female body for implantation if an egg is fertilized that month. If implantation occurs, progesterone levels skyrocket, and if there is no fertilized egg these levels will drop off, which stimulates your body to shed the endometrial lining - aka your period comes. Progesterone is mainly produced by the corpus luteum only after ovulation, and somewhat by the adrenal glands.

The Phases of the Menstrual Cycle

Similar to how one year has four seasons (well, if you live outside of Arizona, at least!), our menstrual cycle has four unique phases: menstrual, follicular, ovulatory, and luteal. These phases not only bring forth a unique set of hormonal fluctuations, but they also affect how we eat, clean, work, love, create, etc. Becoming more in tune with your body and these cycles can open you up to the advantages that certain times of the month can offer you and give you more insight on how you can better plan your time with this knowledge.

Note: if you are on any sort of hormonal birth control, your body is not cycling through these four phases.

Phase 1: Menstruation Phase

Your period marks the beginning of a new menstrual cycle. It typically lasts for 2-7 days depending on the woman. For most of us, about 90% of the blood loss will occur within the first 3 days. During this phase, your estrogen level is at its lowest and you actually haven’t made any progesterone yet this cycle because you have yet to ovulate.

Phase 2: Follicular Phase

The follicular phase is when your body begins to prepare for ovulation. Your period has just ended and this is often when women feel their most energized and creative. To get a little more scientific, each of your ovaries are filled with hundreds of thousands of follicles (a sac of cells that contains an immature egg in the center) that you’ve had since you were born. During the first week of your cycle, a part of your brain called your pituitary gland stimulates a hormone called FSH, or Follicle Stimulating Hormone. This hormone stimulates the growth of these follicles, which release estrogen into the bloodstream. This allows your uterus to respond by building up the inner uterine lining, called the endometrium where fertilization will occur if it’s going to.

After your period has ended, one of those follicles (or sometimes two, hello twins!) becomes the dominant follicle and continues to grow and nourish the egg inside of it, while the other ones begin to degenerate. At this point, we are coming up close to ovulation and that follicle is preparing to rupture and be released from the ovary.

Phase 3: Ovulatory Phase

We’ve now made it to the middle of the menstrual cycle! Two days before ovulation, the follicle that we were just speaking about secretes a surge of estrogen into the bloodstream, which then stimulates the release of LH, or Luteinizing Hormone. Around day fourteen, the LH causes a rapid growth in that follicle and it ruptures, thus releasing the egg that was held inside. This process is what we call ovulation. Some women can physically feel ovulation occur and may report mild to severe pain on one side of their lower abdomen, which can alternate sides each month. That egg then travels down the fallopian tube and into the uterus to get ready for fertilization. Once this egg is released it will live anywhere from 12-24 hours waiting to be fertilized by sperm. It is important to note that a woman’s fertile period is 5 days before ovulation and up to 1 day after, so whether you’re looking to get pregnant or not, you can use this information to your advantage.

The ruptured follicle then becomes what is known as the corpus luteum, which is an endocrine gland that secretes progesterone. Remember, ovulation is an all-or-non event - it either happens or it doesn’t. For proper hormone balance, we want to ensure ovulation is occuring because that is how the body makes progesterone. At this time, testosterone is also spiking, so it is likely the time of the month where you feel the most interested in sex.

Phase 4: Luteal Phase

The fourth phase that we have that rounds out our menstrual cycle is the luteal phase. As we just mentioned above, the corpus luteum has now produced progesterone, which stops the release of FSH and LH so that another egg isn’t released. It also allows the inner uterine lining to become ready for implantation of a fertilized egg, if there is one present. Progesterone will spike about 7 days after ovulation, which is between day 19-21 of a 28 day menstrual cycle. Estrogen and testosterone will also rise a little bit at this time as well. If there is no fertilized egg, the corpus luteum becomes reabsorbed after 12-14 days and progesterone levels decline, which stimulates menstruation. If there is a fertilized egg, then the progesterone and estrogen levels will continue to rise.

I hope that this post has shone some light on how amazing and knowledgeable the female body is and why you can feel very different throughout the month. If you’re interested in learning more about each of these phases in terms of energetics, I will be writing another blog post soon with information like:

  • What foods and exercises support each cycle phase

  • How your phase affects sex, intimacy, and lubrication

  • What changes can you notice in your skin relative to your current phase

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