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Chapter 03: The Menstrual Cycle

Oct 03, 202410 min read

Reference

Salustiano, R. (2024). The Menstrual Cycle. In Dr. RPS Maternal & Newborn Care: A Comprehensive Review Guide and Source Book for Teaching and Learning (2nd ed., pp. 50-63). C&E Publishing, Inc.

The menstruation is a series of rhythmic reproductive cycle that begins from the onset of menstrual bleeding to the day before the next bleeding day. It is characterized by changes in the ovaries and the uterus, influenced by normal hormonal variation mediated by the hypothalamus and anterior pituitary gland (APG) via a negative feedback mechanism. This cycle functions to prepare for the release of egg, fertilization, and implantation.

  • Begins recurring cyclically at puberty with the first menstruation called menarche and ceasing at menopause.
  • The duration of the cycle is highly individualized, but the average/mean cycle length is 28 days; as short as 21 days or as long as 40 days. The regularity of the cycle is also individualized, as some experience irregular (fluctuating length) cycles.
  • The only fairly constant interval is the time from ovulation to the beginning of menses, which is almost always 14 to 15 days.

Hormonal Control of the Menstrual Cycle

  1. Hypothalamic Hormones: the hypothalamus secretes gonadotrophin-releasing (GnRF/GnRH) or inhibiting factors (GnIF) that stimulate the pituitary gland to secrete or inhibit the secretion of corresponding gonadotrophins (Gn).
  2. Anterior Pituitary Hormones (APG): the producer of gonadotrophins (Gn), follicle-stimulating hormones (FSH), and luteinizing hormone (LH).
    • FSH is secreted in response to the hypothalamic follicle-stimulating hormone releasing factor (FSHRF) triggered by low blood levels of estrogen during the first half of the menstrual cycle. Estrogen, by the fourth to fifth day, is at its lowest in a regular 28-day cycle.
    • LH, also called interstitial-cell stimulating hormone, is secreted in response to the hypothalamic luteinizing hormone releasing factor (LHRF) triggered by low blood levels of progesterone. Progesterone, by the thirteenth day, is at its lowest. Progesterone is responsible for the rise in basal body temperature found on the fourteenth day, and the drop on the thirteenth day in a regular 28-day cycle.
  3. Ovarian Hormones: Estrogen and Progesterone
    • Estrogen is secreted by the ovaries, adrenal cortex, and placenta (during pregnancy).
      • It is responsible for the development of secondary sexual characteristics
      • Assists in the maturation of ovarian follicles
      • Inhibits secretion of FSH (negative feedback)
      • Stimulates secretion of LH (positive feedback)
      • It is responsible for the proliferative phase of the menstrual cycle.
      • It is responsible for the fertile cervical mucus that is conducive to fertilization; the change of cervical mucus to thin, clear, colorless, stringy, stretchable, slippery, and lubricative, returning a positive ferning test.
      • In pregnancy, it increases vascularization, maintains the highly-specialized endometrium (decidua), stimulates uterine muscle contraction, causes fatigue, and antagonizes insulin.
    • Progesterone is secreted by the corpus luteum (non-pregnant/early pregnancy) and placenta (as early as the sixth week of pregnancy until parturition)
      • Inhibits secretion of LH (negative feedback)
      • Helps maintain the endometrium by facilitating the secretory phase of the menstrual cycle in preparation for nidation (implantation)
      • Relaxes smooth muscles, including the myometrial muscle of the uterus:
        • Maintains pregnancy by maintaining decidua. If progesterone levels drops in pregnancy, abortion (early pregnancy) or premature labor (late pregnancy) may occur.
        • One of the main theories of labor onset is when progesterone levels drop at term, giving way for the myometrium to contract easily from stimulation by rising stimulants such as oxytocin and prostaglandin.
      • Increases body temperature (Thermogenic)
      • Water-retaining, anti-diuretic action; decreases hemoglobin and hematocrit levels
      • Increases fibrinogen level, increasing coagulability
      • Responsible for infertile cervical mucus: thick, opaque, sticky, non-stretchable
      • Antagonizes insulin along with estrogen, human placental lactogen (HPL), and cortisol.
  4. Prostaglandin: fatty acids recognized as a hormone secreted by a lot of body organs, including the endometrium of the uterus. This affects the menstrual cycle and contributes to stimulating uterine muscles for contraction

Stages/Phases of the Menstrual Cycle

  1. Menstrual Phase or the Bleeding Phase, also known as menstruation. Day 1 to 4, lasting for 3 to 5 or 4 to 6 days. It is the terminal phase of the cycle.
    • Characterized by vaginal bleeding as the uterine endometrium is shed down to the basal layer along with blood from the capillaries and with the unfertilized ovum.
    • Periodic discharge of blood, mucus, and cellular debris from the uterine mucosa and occurs at regular, cyclic, and predictable intervals from menarche to menopause.
    • The period of absolute infertility
    • Menarche is the first onset of menstruation, occurring between 12 to 13 years of age; usually anovulatory, infertile, and irregular.
    • 25 to 60 mL of blood, with about 0.4 to 1.0 mg of iron is lost every day.
    • Menstrual blood is incoagulable due to fibrinolytic activity.
  2. Follicular/Proliferative Phase: Day 5 to 14, ending in ovulation; lasts about 9 days.
    • This phase is controlled by estrogen, where the endometrium thickens by 8 to 10 times during the first few days, known as the regenerative phase.
    • After changes level off at ovulation, the endometrium consists of three layers:
      • Basal Layer: 1 mm, thick, never alters
      • Functional Layer: 2.5 mm, contains tubular glands, consistently changes according to hormonal influences of the ovary
      • Cuboidal Ciliated Epithelium Layer: uppermost layer, covers the functional layer, and dips down to line the tubular glands
    • Ovulation is present in the middle of the cycle; monthly growth and release of a mature, non-fertilized ovum from the ovary. It is the period of absolute fertility. This usually occurs 13 to 15 (average of 14) days prior to the next cycle. At this point, estrogen is high while progesterone is low.
      • Signs of ovulation include breast tenderness, slight rise in BBT (0.3°C to 0.5°C; 0.4°F to 0.8°F) preceded by a slight drop (0.2°F) 24 to 36 hours before, related to changes in progesterone levels.
      • The most fertile time is 3 to 4 days before and 1 to 2 days after ovulation.
      • Positive Spinnbarkeit/Creighton/Billings/Cervical Mucus Test
      • Mittelschmerz, left or right lower quadrant pain corresponding to the rupturing of the Graafian follicle.
      • Positive Ferning Test
    • Estimating ovulation time: subtract 14 days from the menstrual cycle length e.g. it occurs on the 14th day in a 28-day cycle, and on the 16th day in a 30-day cycle.
      • The period of fertility is calculated as five days before and two days after the day of ovulation. In a 28-day cycle, the period of fertility is from 9 to 17th day counting from the first day of bleeding.
  3. Luteal/Secretory Phase: Day 15 to 28; lasts about 12 days.
    • This phase is initiated by ovulation in response to a surge in LH that promotes the development of corpus luteum from the ruptured follicle, the yellow body that secretes high levels of progesterone and estrogen.
    • Progesterone stimulates the already-proliferated endometrium, causing the functional layer to become thicker (2.5 mm → 3.5 mm), more spongy, and softer with glands becoming more tortuous as the endometrial capillaries get distended with blood in preparation for reception/implantation and nourishment of the fertilized ovum.
      • If fertilization occurs, implantation follows 6 to 9 or 7 to 10 days (average 7 days) after. The corpus luteum lives longer and secretes progesterone and estrogen in early pregnancy, which is later replaced by the placenta. The normal lifespan for the corpus luteum is 10 to 14 days.
      • If fertilization does not occur, the corpus luteum involutes after 7 to 8 days after ovulation, becoming white (corpus albicans) which persists up to 10 to 12 days after ovulation. This causes a drop in estrogen and progesterone, leading to the endometrial ischemic/premenstrual phase.

Menstrual Problems and Disorders

(mostly just skimmed over this)

  1. Premenstrual Syndrome
    • activity with rest (aerobic exercises), relaxation techniques, stress management, pharmacotherapy as prescribed (SSRIs, Progesterone Supplementation)
  2. Amenorrhea: the absence of menstruation; primary if menarche never occurred, and secondary if menses ceased for more than 3 months after a regular cycle has been established. Pregnancy is the most frequent cause of secondary amenorrhea. It may also be related to stress, malnutrition, obesity, and hormonal imbalance (ovarian, pituitary, thyroid, adrenal)
    • Causes of primary amenorrhea include thyroid gland abnormalities (typically hyperthyroidism; first suspect even without other S/S), or other endocrine dysfunctions or problems of the hypothalamus, pituitary gland, ovaries, and uterus; chronic illnesses associated with malnutrition or tissue hypooxygenation.
  3. Dysmenorrhea: in Greek, literally “painful monthly bleeding”. It usually corresponds to the secretory phase of the endometrium indicating that ovulation has occurred; absent when ovulation is suppressed.
    • Primary: pain not associated with other diseases or pathology; treat with rest, heat application, distraction, exercise, hormonal therapy, NSAIDs, and analgesia, especially prostaglandin inhibitors (Ibuprofen) as Prostaglandin F is the main contributor in this disorder. It may also be caused by acute uterine anteflexion, retroflexion, and cervical stenosis.
    • Secondary: pain associated with a malpositioned uterus, PID, IUD, endometriosis, or endometritis
  4. Metrorrhagia: abnormal bleeding between menses/period or intercyclic bleeding. May be related to PID, uterine fibroids, corpus carcinoma, erosion, and cancer of the cervix.
  5. Monometrorrhagia: excessive or prolonged menstrual bleeding that may lead to or cause hypovolemia and anemia.
  6. Menorrhagia: excessive, profuse menstrual flow; may be caused by hormonal imbalance, infection, or uterine tumors.
  7. Oligomenorrhea: infrequent menses.
  8. Polymenorrhea: too frequent menses.
  9. Hypomenorrhea: abnormally short menstrual cycle.
  10. Hypermenorrhea: abnormally long menstrual cycle.

Nursing Implementation

Promptly refer for evaluation and diagnosis if there is excessive menstrual flow, intermenstrual or post-menopausal bleeding, absence of menarche at age 17, and severe pre-menstrual tension syndrome. Promote relief of discomfort from dysmenorrhea through rest, mild sedatives, leg lifts, external heat to the lower abdomen, hot drinks, and treatment as ordered (antiemetics, prostaglandin inhibitors)

Menopause

Menopause is a transitional phase for women marking the end of their reproductive abilities. Menopause is to the climacteric as menarche is to puberty. It occurs between 45 to 50 years in 50% of women; can be from 35 to 60 years with an average of 53 years; not completed until 2 years since the last period.

  • Ovulation ceases two years prior to menopause with some individual variation.
  • Initially, menstruation becomes irregular, then it ceases altogether.
  • The drop in estrogen attributed to menopause causes physical symptoms:
    • Hot flashes: a cluster of symptoms due to vasomotor disturbances related to hormonal changes and cessation of menses. It is characterized by a heat arising in the chest and spreading to the neck and face (caused by vasodilation), sweating, occasional chills, dizzy spells, palpitations, and weakness.
    • Emotional changes, such as mood swings or emotional lability.
    • Sleep disturbances
    • The tendency to obesity is not because of a change in adipose deposits but rather due to increased caloric intake.
    • Sexual drive may not be diminished; it may even improve as the need for contraception disappears.
    • Atrophic changes in the vagina, vulva, and urethra and in the trigonal area of the bladder, which may result in dyspareunia, but can be overcome with lubricating gel, or saliva, the most common vaginal lubricant.
    • The breasts become pendulous and decrease in size and firmness.
    • Long-range physical changes may include osteoporosis associated with low estrogen and androgen levels, lack of physical exercise, and low dietary intake of calcium.
  • Treatment, if necessary, include:
    • Estrogen replacement therapy if there is no history of cancer in the family (this treatment is controversial. Short-term low-dose estrogenic therapy may be used for troublesome vasomotor disturbances (hot flashes). Sustained high-dose estrogen therapy has been reported to predispose women to reproductive tract cancer. Hormonal vaginal creams/lubricants (K-Y jelly) for painful coitus or dyspareunia
    • Vitamin B complex and E for hot flashes and other symptoms
    • Increased calcium and phosphorus intake for osteoporosis intervention
    • Support system to provide emotional support.

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