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Many of us feel we don’t have “normal” menstrual cycles. But the truth is, it’s hard to understand what any of this means without more information on what constitutes a normal period. And while checking in with your doctor is crucial if you do think your period is deviating from the norm, we’ve compiled the stages of a normal menstrual cycle to help you figure it out, including what exactly is happening throughout your menstrual cycle. Here’s what constitutes a normal menstrual cycle and, critically, what doesn’t.
First, what is a period?
The term period is commonly used, though clinicians typically say menstruation or menses. This is the shedding of the uterine lining, through the vagina, and it happens roughly every 28 days (for two to six days), from the onset of puberty through to menopause in those with a uterus.
How do I calculate the length of my period?
When trying to calculate days and timing (often done when trying to conceive or using cycle-tracking for birth control purposes), day one refers to the first day of your period. When to start counting is a little subjective, but most will consider your first full flow day as day one. So, if you had some spotting or light bleeding last night, and full flow today, then count today as day one. The cycle continues until the day before you next start to bleed, which in a regular cycle about 28 days (though your period could still be normal even if it’s up to seven days more or less than that 28-day guideline).
In order to learn more about how "normal" your own menstrual cycle is, tracking your symptoms, period and ovulation can all help and can arm you with information to provide your doctor with if you opt to investigate further.
The stages of a normal menstrual cycle
Early follicular phase
Each one of the premature egg cells in your ovaries is surrounded by a layer of specialized cells (granulosa cells that produce estrogen and thecal cells that produce testosterone) and are all contained within a tiny spherical follicle (called antral follicles). These follicular cells nurture the developing egg and deliver hormone signals and nutrients.
The pituitary gland (in your brain) is always releasing both luteinizing hormone (LH) and follicle stimulating hormone (FSH) in a pulsatile manner. Each cycle, ongoing FSH stimulation prompts a group of antral follicles in the ovaries to start growing. These follicles will also start to produce estrogen which thickens the endometrium. Generally, one follicle among the group is the most responsive to FSH and will become the dominant follicle and, eventually, will rupture to release the ovulated egg (while the others regress and dissolve).
Late follicular phase
As the dominant follicle grows, estrogen levels continue to rise, and when they’ve maintained a concentration of at least 200 pg/mL for a minimum of two days, luteinizing hormone (LH) will start increasing. (You might notice the signs associated with higher estrogen such as breast tenderness and changes in cervical mucus.) When LH reaches a peak (typically around 40 to 60 IU/mL), it triggers the release of the mature egg from the dominant follicle within the ovary. The growing follicle releases a lot of estrogen, and a high sustained estrogen level from the growing dominant follicle is the stimulus for the LH surge that initiates the ovulation process.
Learn more about the signs and symptoms of ovulation.
Ovulation
Ovulation is a process that includes the release of the egg from the ovary as well as the maturation of the egg (which is immature prior to the LH surge and mature once it reaches the fallopian tube). The egg detaches from the follicle wall and releases into the fluid-filled center of the follicle. The growing follicle continues to expand with fluid and thin out its walls until it ruptures, releasing the fluid and the egg from the ovary into the pelvis and towards the fallopian tube. Ovulation typically happens two weeks before day one of your next period.
Early luteal phase
After ovulation, the dominant follicle (which houses the egg) within the ovary will transform into the corpus lutem and it will secrete progesterone to help prepare the uterine lining for a potential pregnancy. Meanwhile, the ovulated egg should reach the distal end of the fallopian tube, hoping to run into a nice group of sperm so that one of them can fertilize it. (If that happens, the developing embryo will then travel down to the rest of the fallopian tube and into the uterus as it evolves into a cleavage-stage and blastocyst-embryo over several days. It will then hatch and try to implant into the endometrium.)
Late luteal phase
Even a viable high-quality egg can only survive for about 24 hours if not fertilized by a sperm. The sperm (which can last up to a few days in the uterus and fallopian tubes) should be present and waiting for the egg if you’re hoping to achieve pregnancy (this is why tracking with an LH surge is so helpful, to ensure sperm is at the tubes prior to actual ovulation). The corpus luteum keeps the progesterone pumping for roughly nine to 11 days after ovulation before breaking down—it essentially has a self-destruct timer unless being rescued by the hCG hormone. (If implantation is successful hCG (the pregnancy hormone) will keep the corpus luteum alive and the progesterone party will continue, keeping the endometrium and supporting the development of the placenta.) If no pregnancy occurs, there will not be any hCG and the corpus luteum will slowly dissolve and, with it, the drop in progesterone will cause a menstrual period to start.
Menstruation
What is commonly referred to as a period is the shedding of the endometrium. During the cycle, estrogen is needed to thicken the endometrium and progesterone is needed to transform the endometrium. When progesterone levels decrease, the cascade of endometrial shedding begins, marking the beginning of menstruation. Menstruation typically lasts for two to six days.
