see also:

• gynaecology
• menstrual cycle

• anovulatory cycles are common and have many causes and many clinical consequences due to failure of the high-fertility phase of ovulation, the typical “peak” in libido and cervical mucus changes (lubrication), failure to create a corpus luteum which would normally produce progesterone and either low oestrogen or unopposed high oestrogen
• although may have regular cycles, most are frequently accompanied by either amenorrhoea or irregular menses (due to oestrogen breakthrough bleeding)
• fatigue, stress, weight gain, low libido and relationship issues, vaginal dryness and mood swings are common features
• those with polycystic ovary syndrome (PCOS) will have additional clinical issues including androgen excess features and metabolic issues
• young women with suppressed HPO may also have orthostatic hypotension and other features
• those with hyperprolactinaemia may also have galactorrhoea, orthostatic hypotension, visual field issues (eg. bitemporal hemianopia if pituitary tumour)
• the general loss of libido, vaginal dryness, irregular menses, osteoporosis risk, etc can be partly addressed by hormonal therapy such as OCP but this will not bring back the ovulatory peak in libido

• peri-menarche
  • anovulatory cycles are common after puberty
• suppression of the hypothalamic-pituitary-ovarian axis (HPO)
  • low body weight (eg. < 48kg)
  • high stress levels
  • extreme exercise / relative energy deficiency in sport ¹⁾
  • hypothyroidism or hyperthyroidism
    • thyroid hormones (T3/T4) are essential for proper follicle development, and imbalances alter the production of GnRH, LH, FSH, and prolactin
    • hypothyroid mechanisms:
      • hyperprolactinaemia (see below)
      • reduction of the responsiveness of ovarian granulosa cells to gonadotropins (FSH/LH), resulting in impaired follicular maturation
      • high levels of TSH can directly activate structurally related ovarian FSH receptors, leading to the formation of ovarian cysts and, in some cases, ovarian hyperstimulation
      • low T3/T4 levels can decrease SHBG production, altering the free, active levels of oestradiol and progesterone necessary for a normal cycle
      • it also causes a reduced endometrium response to oestrogen, leading to poor endometrium maintenance and, if fertilization occurs, impaired implantation
    • hyperthyroidism mechanisms:
      • high T3/T4 levels can increase SHBG, which binds to oestrogen, disrupting the free oestradiol levels needed to trigger the LH surge
      • elevated thyroid hormone levels directly disrupt the steroid production within the ovaries, specifically decreasing FSH-stimulated aromatase activity in granulosa cells, which prevents proper follicle development.
      • disrupts the normal pulsatile release of GnRH, causing abnormal LH secretion, which interferes with the ovulatory process
  • hormonal therapies including contraceptives
  • hyperprolactinaemia
    • elevated prolactin inhibits the pulsatile secretion of GnRH, which reduces LH and FSH release from the pituitary, preventing ovulation
    • pituitary prolactinomas
    • lactation
    • hypothyroidism
      • low levels of T3/T4 cause the hypothalamus to increase Thyrotropin-Releasing Hormone (TRH) production to stimulate the thyroid. TRH is a potent stimulator of both TSH and prolactin production.
    • medications especialy anti-psychotics
    • nipple dermatoses
• polycystic ovary syndrome (PCOS)
  • may account for 70% of chronic anovulation
• primary ovarian failure
  • perimenopause
  • menopause

• loss of ovulatory peak
  • loss of the typical “peak” in libido and cervical mucus changes (lubrication)
  • infertility
  • failure to create a corpus luteum
• absence of a luteal phase
  • loss of the usual luteal fluid retention may make them more susceptible to orthostatic hypotension
  • low progesterone levels
    • reduced libido
    • mood issues
    • loss of the normal progesterone withdrawal bleed which in ovulatory cycles causes normal menstruation
• low oestrogen levels in some
  • vaginal dryness and thinner tissue, causing painful intercourse
  • mood issues
  • amenorrhoea
  • increased risk of osteoporosis
• unopposed high oestrogen levels in some
  • irregular oestrogen breakthrough menses which may be heavy if there is substantial build up of secretory endometrial lining (esp. in perimenopause)
  • mood swings
  • uterine cancer