Menstrual cycle: Phases

Menstrual cycle: Phases


The menstrual cycle of a woman goes through four main phases-

  • menstruation
  • the follicular phase
  • ovulation
  • the luteal phase.


It is the process of eliminating the thickened lining of the uterus (endometrium) from the body through the vagina. The menstrual fluid contains blood, cells from the lining of the uterus (endometrial cells) and mucus. The average length of a period is between three days and one week depending varies from one woman to another.

Follicular phase

The follicular phase starts on the first day of the period and ends with ovulation. Prompted by the hypothalamus, the pituitary gland releases follicle-stimulating hormone (FSH). This hormone stimulates the ovary to produce tiny nodules or cysts, which bead on the surface. This can occur around day 10 of a 28-day cycle. The growth of the follicles stimulates the lining of the uterus to thicken in preparation for a possible pregnancy.


Ovulation is the process of releasing a matured egg from the ovary. This usually happens mid-cycle, 2 weeks or so over menstruation starts. After the egg gets released it moves down to the fallopian tube and stays there for 12 to 24 hours

The developing follicle leads to a rise in the level of oestrogen and the brain recognizes these rising levels and releases a chemical called gonadotrophin-releasing hormone (GnRH). This hormone stimulates the pituitary gland to produce luteinizing hormone (LH) and FSH. The egg would be funnelled into the fallopian tube. The typical life span of the egg stays only around 24 hours. The chances of getting pregnant are much higher if you know about your ovulation and fertile window in the menstrual cycle

The Luteal Phase

The egg bursts from its follicle during the ovulation but the ruptured follicle stays on the surface of the ovary. The follicle transforms into a structure known as the corpus luteum for the next two weeks and releases progesterone and a small amount of oestrogen. The uterus maintains a thick lining due to the combination of these hormones, waiting for the fertilized egg to implant.

The fertilized egg implants in the lining of the uterus. The corpus luteum has been maintained with the help of hormonal development. The hormone human chorionic gonadotrophin (HCG) is the one that gets detected in a urine test for pregnancy. The corpus luteum keeps producing the raised levels of progesterone that are needed to maintain the thickened lining of the uterus.

The corpus luteum weakens and dies if the pregnancy does not occur, usually around day 22 in a 28-day cycle. The lining of the uterus falls away due to a drop in progesterone levels causing the lining of the uterus to fall away and that’s when periods occur. The cycle then repeats.