Understanding Your Period: Why Menstrual Flow Happens Monthly

Menstruation is the monthly shedding of the uterine lining (endometrium) when pregnancy does not occur. It is the visible phase of the menstrual cycle, orchestrated by hormonal fluctuations.

Cycle Phases (28-day average)

1. Menstrual (Days 1–5) – progesterone drop → spiral artery vasoconstriction → endometrial shedding.
2. Follicular (Days 1–13) – FSH stimulates follicular growth; rising estrogen rebuilds endometrium.
3. Ovulation (Day ~14) – LH surge triggers egg release.
4. Luteal (Days 15–28) – corpus luteum secretes progesterone; endometrium becomes secretory, ready for implantation. If no pregnancy, corpus luteum regresses → progesterone falls → menstruation restarts.

Key Hormones

• GnRH (hypothalamus) → FSH/LH (pituitary) → estrogen/progesterone (ovary).

Variations

Cycle length 21–35 days is normal. Flow 3–7 days, 30–80 mL. Irregular cycles common in adolescence, perimenopause, PCOS, thyroid disorders, stress, weight changes.

Track cycles; consult clinician if cycles <21 or >35 days, heavy bleeding (>80 mL or soaking pad/tampon hourly), severe pain, or absent periods >3 months (not pregnant).