The Fifth Vital Sign: The Menstrual Cycle

Is the menstrual cycle really that important that it should be considered the fifth vital sign?? To answer this question, it is important to understand exactly what a vital sign is. Vital signs are measurements of your bodies most essential (what keeps you alive) functions. There are four vital signs: Pulse (heart rate), Blood Pressure, Body Temperature, and Respiration Rate (rate of breathing). Many doctors will also check blood oxygen saturation with a pulse oximeter as part of your vitals. All of these measurements can detect and monitor both acute and chronic conditions, such as hypertension (high blood pressure), and fever (body temperature >100.4 F). Now that you know the importance of vital signs, do you think the menstrual cycle should be included? I think so, and I'm going to explain why.

An abnormal menstrual cycle can indicate serious underlying medical conditions such as cancer, fibroids, fibromyalgia, bleeding disorders, thyroid dysfunction, and STI's. Knowing the difference between what is normal and abnormal during menstruation can help women catch these conditions early. Your cycle also effects the function of your circulatory system, immune system, and water/electrolyte balance. If that's not enough reason to consider the menstrual cycle as a fifth vital sign then read on, I have another fact that is sure to solidify this point.

Did you know that menstrual blood contains stem cells? Yes, you read that correct. Menstrual blood has similar regenerative capabilities as the stem cells in umbilical cord blood, adipose tissue, and bone marrow. Stem cells are the foundation for every organ and tissue in your body. These special cells have the ability to develop into many different cell types, from muscle cells to brain cells. In medicine, they are used to repair damaged tissues. Menstrual stem cells have demonstrated the capability of differentiating into many other types of stem cells such as cardiac, pulmonary, neural, bone, fat and cartilage. Currently, they are being studied to treat stroke, heart disease, diabetes, neurodegenerative disease (such as Alzheimer's), and ischemic wounds in pre-clinical and clinical trials. Now if this doesn't illustrate how powerful your period is, I don't know what to tell you!


The Menstrual Cycle 101

The menstrual cycle is a sequence of changes a woman's body goes through monthly in preparation for the possibility of pregnancy. In order for the menstrual cycle to occur your brain, ovaries, and uterus communicate with one another through hormones (chemical signals sent through the blood from one part of the body to another). Each month, an egg is released from one of your ovaries, while simultaneously hormonal changes prepare the uterus for pregnancy. If ovulation takes place and the egg isn't fertilized, the lining of the uterus sheds through the vagina. This is a snapshot of the menstrual cycle, now lets get into the details so you really know what's going on.

Before we delve in here are some terms that you should know:

  • Menstruation "The period": Normal vaginal bleeding that occurs from the shedding of the uterine lining. Last from 3-7 days on average.

  • Menses: Blood and pieces of cellular tissue discharged from the uterus at menstruation.

  • Menstrual Cycle: The number of days between the first day of menstruation to the onset of menstruation of the next cycle. A complete cycle is typically between 25-30 days, however, cycles are individualized and vary from person to person.

  • The Follicular Phase: Follicles grow and prepare for ovulation. This begins on the first day of the period and ends when ovulation occurs.

  • Ovulation: An ovary releases a mature egg down the fallopian tube to be fertilized. Shortest phase of cycle, last 24 hours.

  • The Proliferative Phase: The second phase of the uterine cycle when estrogen causes the lining of the uterus to grow, or proliferate. Building it back up after menses.

  • The Luteal Phase: The time between ovulation and before the start of menstruation. The mature egg released during ovulation travels down the fallopian tube, where it may come in contact with sperm and be fertilized. The follicle itself then changes and transforms into a new structure called the corpus luteum. The luteal phase usually last for 14 days.

  • The Secretory Phase: The uterine lining produces chemicals that will either help support an early pregnancy or will prepare the lining to break down and shed if pregnancy doesn’t occur.

****Ovarian Cycle vs. Uterine Cycle: Throughout the menstrual cycle there are changes taking place in both the ovaries and the uterus simultaneously. The two notable phases of the menstrual cycle are the The Ovarian cycle consists of the follicular phase, ovulation, and luteal phase. The Uterine cycle is divided into menstruation, proliferative phase, and secretory phase

The Phases of The Menstrual Cycle



  • Location: Uterus

  • What Happens: Old blood and tissue from the uterus lining is shed through the vagina and cervix.

  • Time: Last from 3-7 days on average.

Follicular Phase:

  • Location: Ovaries

  • What Happens: The follicular phase starts on day 1 of the period. During menstruation, the the hypothalamus (hormone control center), sends a message to your pituitary gland (a small area at the base of the brain that makes hormones) to produce the hormone follicle stimulating hormone or FSH. FSH communicates with the ovaries, and tells them to prepare an egg for ovulation (release of an egg from the ovary). There are many follicles (fluid filled sacs containing eggs) in each ovary at different stages of development. About halfway through the follicular phase (around the end of menses), one follicle in one of the ovaries grows to about 1 cm. This follicle becomes the dominant follicle and is prepared to be released at ovulation. The other follicles start to wither and are reabsorbed into your body. The dominant follicle produces estrogen as it grows, which peaks just before ovulation occurs.

  • Time: Occurs from first day of menstruation to ovulation. For most women, the follicular phase lasts 10-22 days, but this can vary from cycle-to-cycle.

Proliferative Phase:

  • Location: Uterus

  • What Happens: While the ovaries are working on developing the egg-containing follicles, the uterus is responding to the estrogen produced by the dominant follicle. The increase in estrogen rebuilds the lining of the uterus that was just shed during the last period. The lining becomes rich in nutrients to prepare for a possible pregnancy. This is called the proliferative phase because the endometrium (the lining of the uterus) becomes thicker or proliferates. The endometrium is thinnest during the period, and thickens throughout this phase until ovulation occurs.

  • Time: This occurs from the end of the period until ovulation begins

Ovulatory Phase


  • Location: Ovary

  • What Happens: The dominant ovarian follicle continues to grow in size to about 2-3cm. As it grows it produces more and more estrogen. When estrogen levels are high enough, it signals the brain to increase the hormone production of lutenizing hormone or LH. This spike results the release of the egg from the ovary, also known as, ovulation. The egg is also known as an ovum, oocyte, or female gamete. The egg travels down the fallopian tube where it can be fertilized by sperm.

  • Time: Occurs in middle of the menstrual cycle, usually about 13-15 days before the next period. The timing varies for each woman, and it may even vary from month to month for women with irregular menses.


The Luteal Phase

  • Where: Ovary

  • What Happens: Once ovulation occurs, the egg travels down the fallopian tube where it then changes into a new structure called the corpus luteum. The corpus luteum produces progesterone, as well as, estrogen. Progesterone levels peak about halfway through this phase. If an egg is fertilized, progesterone from the corpus luteum supports the early stages of pregnancy. If no fertilization occurs, the corpus luteum will start to deteriorate between 9 and 11 days following ovulation. This results in a drop in estrogen and progesterone levels, which will results in menstruation.

  • Time: From the end of ovulation to the start of the next period. This phase typically last about 14 days.

Secretory Phase

  • Where: Uterus

  • What Happens: Rising levels of progesterone from the corpus luteum cause the endometrium to thicken the lining of your uterus so that a fertilized egg can implant. Blood vessels grow inside the lining to supply oxygen and nutrients to the potential embryo. During the secretory phase the endometrium produces and releases (secretes) many chemical messengers. Prostaglandins are a chemical messenger that causes the uterine muscle to contract (cramps). The cramping caused by this prostaglandin helps to stimulate the period. If a pregnancy occurs, prostaglandin production is inhibited. If a pregnancy does not occur, menstruation begins and the whole cycle starts over again.

  • Time: From ovulation to the start of the next period


  1. The menstrual cycle starts with the first day of menstruation (the period) and ends when the next period begins.

  2. Hormone signals are sent back and forth between the brain and the ovaries, causing changes to the sacs in the ovaries that contain eggs (follicles) and the uterus

  3. The first part of the cycle prepares an egg to be released from the ovary and builds the lining of the uterus

  4. The second part of the cycle prepares the uterus and body to accept a fertilized egg, or to start the next cycle if pregnancy doesn’t happen

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