What are the phases of the menstrual cycle anyway?
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Not everyone knows that the menstrual cycle starts with the first day of your period and ends on the first day of your next period. Another fact not everyone knows is what is considered normal for menstrual cycle length. The 28-day cycle you may be familiar with is actually an average, so some cycles are longer and some are shorter. In fact, the length of the menstrual cycle can vary from person to person AND from cycle to cycle for each individual throughout life (2). The ‘normal range’ for a cycle is anywhere from 21 to 35 days. So if your average cycle is 35 days long, that is still considered normal (1). Cycle length may be affected by a bunch of factors like age, genetics, smoking, diet, exercise, stress levels (2, 3)… So basically, all the things.
We’re going to talk about all that another time, but for today, let’s back up and cover the basics. The menstrual cycle consists of 3 phases: the follicular phase, the ovulatory phase, and the luteal phase (4).
The follicular phase starts on the first day of your period and ends on the day of ovulation. This phase is so named because follicle stimulating hormone (FSH) causes about 15 to 20 eggs to begin maturing in each ovary, which are enveloped in their own follicle (5), a fluid-filled sac (6). The greatest variation in any given cycle will usually be in this phase. That’s because the maturation process can last anywhere from 8 to 21 days, but eggs take about 2 weeks to mature on average (5).
During this phase, your basal body temperature (BBT), which is basically your temperature immediately upon awakening, tends to be lower, and you may not have any cervical mucus (CM) or your CM may be sticky and tacky (7).
The increased amount of estrogen released by the follicle causes a few different things to happen in your body. Your cervix and the ligaments holding it in place respond to changes in response to estrogen, lifting it higher, and softening and opening it to allow sperm to pass through. If you’re charting your cycle and tracking cervical position, you’ll feel the progression and a palpable difference, especially around ovulation. Estrogen is also what makes the egg from the largest follicle to push through the wall of the ovary, which leads us to the next phase (5).
An increase in luteinizing hormone (LH), called the LH surge, will also be triggered up to 36 hours before the egg is released; this is when the ovulation phase begins (9).
Ovulation is the release of a mature egg from the ovary. When LH reaches its peak, the egg will be released about 10 to 12 hours later (9). In the days leading up to and on the day of ovulation, you may experience more fertile CM, characterized by higher water content. It may be egg white CM, which is stretchy and looks exactly like it sounds, or it may be so watery that the only evidence is a circular wet patch on your underwear (5, 7).
After the egg is released, the follicle that housed the mature egg collapses, becoming the corpus luteum (meaning “yellow body”), and starts to release progesterone. The other eggs and follicles that had begun developing will disintegrate (5).
The day after ovulation, the increase in progesterone causes your BBT to spike, which is referred to as the temperature shift. When this shift from low to high temperatures is sustained for at least 3 days, it suggests that ovulation occurred, however, in some individuals, ovulation may happen without this temperature spike (8).
The luteal phase starts the day after ovulation (the same day as the temperature shift) and ends on the day before your period. The corpus luteum has a limited lifespan of about 12 to 16 days, which is why the luteal phase has less variation than the follicular phase (2). The corpus luteum releases many different hormones, but progesterone dominates this phase (10) and is the reason that higher BBTs are sustained until the start of your period (11).
In response to progesterone, the endometrium, or lining of the uterus, thickens to prepare for implantation and pregnancy (10). The lower levels of estrogen causes your cervix to drop, become firm, and close up (12). Your CM will also start to dry up, and you may not see any more until after your period; though, you may experience some fertile-quality CM during the luteal phase (5).
If the egg is fertilized and becomes an embryo, that’s a whole different story! Your body will use the lining that was developed since the embryo will implant in the uterus (13), the corpus luteum will live on (14), and the pregnancy will progress in a whole other amazing process.
So there you have it: the menstrual cycle in a nutshell. With up to 21 days for the follicular phase and 16 days for the luteal phase, that’s quite different from the 28-day cycle we’re all led to believe we should have. Definitely check with your doctor if you are concerned about your health, but if your cycles aren’t 28 days, that’s ok — you do you (3)!
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Like we always say: knowledge is power, and we want you to be informed about your health. If you loved this article, sign up here for our educational email series all about learning to chart with Kindara. Plus, Kindara automatically calculates your cycle lengths and averages — no guesswork or math! — so you’ll be able to easily see your own patterns and what’s normal for your body.