The menstrual cycle is a natural biological process involving coordinated changes in the ovaries, uterus and reproductive hormones. Although it is often described as a 28-day cycle, there is considerable variation between women and even between different cycles in the same woman.
What is the menstrual cycle?
The menstrual cycle prepares the female reproductive system for the possibility of pregnancy.
The first menstrual period, known as menarche, usually occurs during adolescence. The timing varies according to several factors, including genetics, nutrition and environmental influences.
A menstrual cycle is counted from the first day of one period to the first day of the next. Although 28 days is commonly used when explaining the cycle, actual cycle length varies considerably between individuals.
The cycle, basically, has four consecutive stages which are:
1. Menstruation
Approximately days 1–5
Menstruation occurs when the lining of the uterus, known as the endometrium, is shed.
At this stage, levels of the hormones oestrogen and progesterone are relatively low.
Menstrual bleeding marks the beginning of a new cycle.
2. Follicular phase
Beginning on day 1 and continuing until ovulation
During the follicular phase, the pituitary gland releases follicle-stimulating hormone — FSH.
FSH stimulates follicles within the ovaries to develop. Each follicle contains an immature egg.
As the dominant follicle develops, it produces increasing amounts of oestrogen. Oestrogen encourages the lining of the uterus to grow and prepare for the possibility of pregnancy.
3. Ovulation
Ovulation occurs when a mature egg is released from the ovary.
A rapid rise or surge in luteinising hormone — LH triggers ovulation.
In a textbook 28-day cycle, ovulation is often described as occurring around day 14. In real life, however, the exact timing can vary considerably between women and between individual cycles.
This variability is important because it means that simply counting calendar days is not a completely reliable way of predicting either ovulation or the days on which pregnancy is possible.
4. Luteal phase
After ovulation, the follicle that released the egg becomes a temporary hormone-producing structure called the corpus luteum.
The corpus luteum produces progesterone, which helps maintain and prepare the uterine lining for implantation of a fertilised egg.
If pregnancy does not occur, the corpus luteum breaks down. Progesterone and oestrogen levels fall, the uterine lining is shed and another menstrual period begins.
Four important menstrual hormones
Four hormones play particularly important roles in controlling the cycle:
FSH — Follicle-Stimulating Hormone
FSH is produced by the pituitary gland and stimulates ovarian follicles to develop.
LH — Luteinising Hormone
LH is also produced by the pituitary gland. A surge in LH triggers ovulation.
Oestrogen
Oestrogen is predominantly produced by the developing ovarian follicle during the first part of the menstrual cycle. Among its functions is stimulating growth of the uterine lining.
Progesterone
Progesterone is mainly produced by the corpus luteum following ovulation. It prepares and maintains the uterine lining for a possible pregnancy.
Together, these hormones form part of the hypothalamic-pituitary-ovarian axis, the hormonal communication system responsible for coordinating reproductive function.
When can pregnancy occur?
Pregnancy is most likely during the fertile window surrounding ovulation.
Women wishing to avoid pregnancy should discuss appropriate contraceptive methods with a healthcare professional.
Physical symptoms during the menstrual cycle
Changes in reproductive hormones may be associated with various physical symptoms.
These can include:
- abdominal or pelvic cramps
- breast tenderness
- bloating
- headaches or migraine
- tiredness or reduced energy
- changes in appetite
- changes in sexual desire.
The intensity of these symptoms varies greatly. Some women experience very few symptoms, while others experience significant disruption to work, education, exercise or everyday activities.
Mood and emotional changes
The menstrual cycle can also influence emotional wellbeing.
Symptoms such as written below can occur in varying degrees (or not at all):
- irritability
- mood changes
- anxiety
- tension
- reduced concentration
- low mood.
For some women these symptoms occur predictably during the second half of the menstrual cycle and improve shortly after menstruation begins.
This pattern may represent premenstrual syndrome — PMS.
A smaller number of women experience significantly more severe psychological symptoms during their menstrual cycle. Therefore, significant cyclical depression, anxiety, or marked functional impairment should not be dismissed as “normal period symptoms” and may warrant medical evaluation.
Changes in sexual desire
Sexual desire may also change during the menstrual cycle.
Some women describe increased sexual interest around the time leading up to ovulation, whereas others notice little difference.
During menstruation or the premenstrual phase, symptoms such as pain, bloating, fatigue or mood changes may reduce sexual desire.
However, these effects vary considerably and should not be assumed to occur in every woman. Sexual wellbeing is influenced by many psychological, social, relationship and biological factors in addition to reproductive hormones.
What menstrual changes warrant medical evaluation?
Amenorrhea:
Amenorrhea is the absence of menstruation.
It can occur when periods never start as expected or when previously occurring periods stop for an extended period.
Pregnancy is a primary consideration for someone of reproductive age whose periods unexpectedly cease.
Infrequent periods:
Long intervals between periods may result from conditions affecting ovulation, such as polycystic ovary syndrome, thyroid disorders, and other hormonal imbalances.
Frequent or irregular bleeding:
Some women experience unusually short cycles or bleeding between expected menstrual periods.
Persistent or unexplained bleeding should be evaluated rather than assumed to be a normal variation.
Heavy menstrual bleeding:
Heavy menstrual bleeding significantly interferes with a woman’s physical, social, emotional, or daily life.
Symptoms may include frequent changes in menstrual protection, flooding through clothing or bedding, passing large clots, or developing symptoms of iron-deficiency anemia.
Dysmenorrhea:
Dysmenorrhea refers to painful menstruation.
Mild cramping is common, but severe or progressively worsening period pain may occasionally be associated with conditions like endometriosis or adenomyosis and should be investigated appropriately.
The article identifies hormonal disorders, thyroid disease, stress, substantial weight changes, and certain medications as factors that can affect menstruation.
Menstrual hygiene and self-care
Good menstrual care is primarily about comfort, hygiene and access to appropriate menstrual products.
Pads, tampons, other products can all be appropriate depending upon personal preference and circumstances.
Helpful measures include:
- changing menstrual products at appropriate intervals
- washing hands before and after changing products
- maintaining normal external genital hygiene
- staying hydrated
- eating a balanced diet
- maintaining regular physical activity where comfortable
- obtaining adequate sleep
- using appropriate pain relief when needed
- seeking medical advice when symptoms significantly interfere with normal activities.
The review also suggests that exercise, stress management and tracking symptoms may help some women manage menstrual symptoms.
An important note about intimate hygiene
The vagina is self-cleaning, and internal vaginal washing or douching is generally unnecessary.
Good menstrual hygiene usually requires normal washing of the external genital area — the vulva — with water and gentle products where desired, rather than attempting to clean inside the vagina.
When should you seek medical advice?
Medical assessment should be considered if you experience:
- very heavy menstrual bleeding
- periods that suddenly become substantially different from your usual pattern
- bleeding between periods
- bleeding after sex
- severe period pain
- prolonged absence of periods when pregnancy is not the explanation( great than 3 months of no periods)
- persistent irregular cycles
- symptoms suggesting significant anaemia, such as marked tiredness or breathlessness
- significant emotional or psychological symptoms linked to the menstrual cycle
- menstrual symptoms that substantially interfere with everyday life.
Irregular & Regular Cycles- Definition.
Remember: Menarche is the FIRST menstrual period of a young girl or woman.
It is usually irregular in the early ages (around 10- 16years, tends to become regular for most women 17 – 40-45years, irregular thereafter and then ceases(Menopause) altogether at at average age of 51yrs(UK figures). These are approximate figures.
| Time since menarche | Cycle characteristics | Ovulation status |
| Initial onset | Irregular, variable length (21-45 days in 90% of girls) | Mostly anovulatory |
| First 2 years post-menarche | Highly variable cycles, Irregular | Approximately 50% anovulatory |
| By year 3 post-menarche | More regular: 21-24 days in 60-80% of girls | Increasing ovulatory cycles |
| By year 5 post-menarche | 21-34 day cycles are more typical. Regular | Approximately 25% are still anovulatory |
| Several years later | Adult-like cycle patterns | Anovulatory cycles decrease to approximately 20% |
Primary amenorrhea by age 15 or > 3 years post thelarche (breast development):- -Absence of menstruation by age 15 or 3 years after breast development.
We will revisit this topic in detail at a later post.