Hormones & Cycles

The Phases of the Menstrual Cycle

Many of us think that period and menstrual cycle are the same things, but they are not. Most healthcare professionals agree that the menstrual cycle can be divided according to the “ovarian cycle” and the “uterine cycle”. The period belongs to the uterine cycle and it is just a phase of it. Here we will learn the differences between the two cycles and their phases.

The ovarian cycle, probably the most widely known type, is divided into follicular, ovulation, and luteal phases. At the same time, the uterus goes through a cycle as well, where the period is experienced. This is known as the uterine cycle; the phases are menstruation, proliferative and secretory.

The ovarian and uterine cycles overlap and interact to prepare for a potential pregnancy every month. We have grouped them into four parts to see how they interact.

menstruation menstrual cycle

Part 1

Uterine Cycle: Menstruation

Length: Usually 3-5 Days

Day 1 of your period and menstrual cycle is the first bleed day (not spotting). Menstruation is the normal shedding of blood and tissue through the cervix and vagina. The tissue that is shed is the endometrium (uterine lining).

Ovarian Cycle: Follicular Phase

Length: 9-22 days (very variable)

The follicular phase includes menstruation. It lasts from period to ovulation. During your period Follicle Stimulating Hormone (FSH) levels start to rise which tells the ovaries to prepare an egg for ovulation. Follicles are small fluid-filled sacs in the ovaries that contain immature eggs. Every cycle follicles are activated but only one predominant follicle is selected. The dominant follicle then grows to around 20 mm and is released at ovulation.

Even though FSH levels rise during the follicular phase, they do decrease slightly around 5-6 days before ovulation (This is why Pearl tests FSH in addition to LH to predict ovulation in advance).

proliferative phase of the uterine cycle

Part 2

Uterine Cycle: Proliferative Phase

This phase occurs from when your period ends until ovulation. The uterine lining is the thinnest during your period. After that, as estrogen levels rise the endometrium becomes thicker. This happens because the uterine lining starts to prepare for possible implantation of a fertilized egg.

ovulation in the menstrual cycle

Part 3

Ovulation - “The star of the show”

The egg is released from the ovary to the Fallopian Tube

The dominant follicle keeps growing and growing and secreting estrogen. Estrogen levels increase dramatically and when they remain high it signals the brain, which causes lh (LH) levels to rise and peak. The LH peak triggers ovulation: the egg is released from the ovaries to the Fallopian Tube. the LH peak happens typically 12-24 hours before ovulation.

Learn all about the signs of ovulation here!

It is during this phase that if you take an OPK it will be positive, as LH peaks.

luteal phase

Part 4

Ovarian Cycle: Luteal Phase

Length: 12-14 days

The luteal phase begins after ovulation and ends when your new period begins. The follicle that contains the egg transforms into the corpus luteum. A temporary endocrine gland that releases progesterone and estrogen. Levels of progesterone rise during this phase confirming ovulation.

Low progesterone levels can lead to a shorter than normal luteal phase, which is typical in Luteal Phase Defect. A Luteal Phase Deficiency can cause miscarriages, difficulty getting pregnant and spotting between periods.

Some women suffer from PMS or Premenstrual Syndrome during this phase. It is thought that it is due to estrogen and progesterone levels dropping when you are not pregnant. However, not every woman suffers from PMS.

secretory phase uterine cycle

Uterine Cycle: Secretory Phase

The endometrium lining reaches its maximal thickness. The hormone which dominates is progesterone. At the end of this phase, progesterone will signal the brain to lower LH and FSH production, so progesterone and estrogen levels also start to decrease. If fertilization does not happen hCG is not secreted and the corpus luteum degenerates.

If fertilization does not happen, then hormone levels drop and a new period begins and a whole new cycle begins.

With Pearl, you can track your hormones, which trigger all the changes in the menstrual cycle. By tracking your cycle with Pearl, you can know when you will ovulate and when your most fertile days are - in advance!

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