The Menstrual Cycle
Understanding your body is important.
Your periods are a part of your body.
Fertility awareness means being aware of your fertility. It also means understanding your body and your hormones, specifically, your menstrual cycle. I‘m bringing it back to the basics talking about your menstrual cycle.
The “cycle” is the number of days from the first day of bleeding of the menses until the last before the start of the next menstrual bleed. When we discuss how many days a cycle is in length - this is what we are referring to. Although normal cycles can range between 25-35 days, each woman should have a more narrow range of what is normal for her (varying by only 1-2 days per month).
The first day of full flow (not spotting) is considered day #1. This starts the first half of the cycle known as the follicular phase.
Imagine you have a vault inside your ovary where all your eggs are kept. When you are born, the vault is full, and when you go into menopause the vault is empty. (It isn’t quite this simple, but I think this is a good analogy to understand what happens).
In the early follicular phase a group of eggs is released from the vault- each egg is inside a follicle. This group of eggs is considered a cohort, from which, one will grow, mature, and ovulate, and the rest will die. The size of the cohort is proportional to how many eggs you have remaining, meaning as you have more eggs left you have a larger number of eggs growing per month and if you have fewer eggs you will have a smaller number released per month. Measuring the size of the cohort is called testing ovarian reserve.
FSH is a well names hormone (follicle stimulating hormone) and it is released from the pituitary gland during the follicular phase which stimulates one follicle to grow (and one egg to mature inside of it).
As the egg matures, estrogen is made. Estrogen stimulates growth of the endometrial lining inside the uterus.
Elevated estrogen levels signal to the brain that the follicle is at maturity and then LH (luteinizing hormone) is released for the pituitary gland in a “surge”. Elevated estrogen levels also result in type 4 cervical mucus - “egg-white” and sticky.
The LH surge is what allows ovulation - ovulation typically occurs about 24-36 hours after the start of the LH surge (and about 12 hours from peak). The LH surge can be detected by ovulation predictor kits (OPKs). Ovulation typically happens the day after the first positive OPK.
The time period from ovulation until the end of the cycle is known as the luteal phase.
In the luteal phase, the follicle that released an egg forms a cyst called a corpus luteum. The corpus luteum makes progesterone which is essential to support an early pregnancy until the placenta is fully formed. Deficiencies in progesterone production can cause a “luteal phase defect” in which the luteal phase may be shortened or may have spotting, potentially impairing implantation. Importantly, progesterone is released in pulsatile fashion (responding to pulsing LH surges during the entire luteal phase) and so there is no blood test to measure “adequate progesterone” in the luteal phase. Testing progesterone in the luteal phase only confirms if a woman did or did not ovulate.
If pregnancy does not occur, then the corpus luteal dies, progesterone levels drop, and bleeding begins - starting the next cycle.