The menstrual cycle is one of the most remarkable events within our bodies. It displays a fine-tuned interplay of hormones and physiological responses. Understanding our periods begins with understanding the menstrual cycle as a whole.
Our period gets all the attention because it’s the part of our menstrual cycles that is the most obvious and, for many, unpleasant. But, in reality, our periods are just one small part of an ongoing physical story. The less apparent events during your menstrual cycle dictate your period symptoms, timing, and even whether you get a period at all.
While the menstrual cycle is intricate, we can easily understand it by learning its two phases.
- The Follicular (or oestrogenic) Phase
The first part of the menstrual cycle begins on the first day of your period and lasts until you ovulate. As we’ll explain below, in the days leading up to your period, the uterine wall (or endometrium) has thickened to about 8-13 millimeters to provide the best conditions to nurture a fertilized egg. When pregnancy does not occur, the unfertilized egg and thickened uterine lining pass out of the body via the vagina.
From day 1 of your follicular phase, your body has already started to produce small but ever-increasing amounts of a hormone called Follicle Stimulating Hormone (FSH). This hormone causes around 15 to 20 eggs, each encased in their follicle, to mature in your two ovaries. These follicles produce the hormone Oestrogen, which is necessary for ovulation. When it’s time to ovulate, the egg from the largest and most dominant follicle will be released, and the remaining eggs will disintegrate.
The follicular phase’s duration can vary considerably from woman to woman and throughout a woman’s lifespan. On average, your Follicular Phase lasts about two weeks, but it can range anywhere from 8 to 21 days or longer to complete.
- The Luteal (or progestational) Phase
After ovulation, your body and hormones switch gears and enter the Luteal Phase. This second phase marks the length between ovulation and the last day before your period. Unlike Follicular Phases, Luteal Phases usually have a finite lifespan of about 12 to 16 days.
After one of your ovaries releases an egg, the follicle that held the egg collapses on itself, becoming what’s called the corpus luteum. The corpus luteum remains on the ovarian wall and releases the hormone progesterone.
Progesterone is a critical hormone in a woman’s menstrual cycle, and it leads the charge during the Luteal Phase. Among many things, it’s responsible for preventing the release of all other eggs during the rest of your cycle. Progesterone also causes the uterine lining (or endometrium) to thicken and sustain itself until the corpus luteum disintegrates about two weeks later.
If the released egg doesn’t become fertilized, progesterone (keeping the endometrial wall nourished and in place) plunges. This hormonal shift causes your period and day one of your next cycle.