Explaining the Menstrual Cycle with Dr. Kate Killoran

Period trackers are helpful for several reasons. The most obvious, of course, is to alert you about bleeding: but, there is a lot more going on in your body that is less obvious yet nonetheless impactful and is also worth tracking. There is a considerable ebb and flow of your hormones every month, which is normal. Understanding this ebb and flow can empower you to figure out why you feel the way you do at different times. It can also help you recognize common syndromes associated with shifting hormones such as PMS, menstrual migraines, and perimenopause.

So, what ultimately happens during your menstrual cycle? What are the hormonal changes that occur every month, and what effect do they have on you?

First off, let's begin by establishing how we count the days in a menstrual cycle. Day one is the first full day of flow. To determine your cycle's length, start with day one, then count every day of that cycle until you come to the first day of flow in your next cycle. Include bleeding days, which I think is the most common mistake people make when talking about their cycles. 

Regular cycles vary in length from 24 - 35 days. We often refer to a 28-day cycle for simplicity's sake. However, most menstruating people do not have a 28-day cycle. They are either shorter, longer, or vary from month to month.

Your cycle has two major phases, follicular and luteal, with a brief but crucial third phase, ovulation, in the middle. Estrogen and progesterone are the primary hormone drivers of the menstrual cycle. They are secreted by the ovary, and are responsible for stimulating the lining of the uterus or womb, called the endometrium, to grow, preparing for a potential pregnancy.

The first phase of your cycle is called the follicular phase; the main event is creating a follicle in the ovary. It is from this follicle that an egg is released, which is known as ovulation. This phase ranges in length but is usually between 12 - 16 days. If your cycles are longer or shorter than the standard 28-day cycle, it is the follicular phase that will vary.

During the first few days of the follicular phase, both estrogen and progesterone are low when you're bleeding. Estrogen levels gradually begin to rise on day 4 or 5 and create a dominant follicle. The dominant follicle prepares the egg for ovulation. Around cycle day ten (in a 28-day cycle), estrogen production increases dramatically, and progesterone slowly rises. Estrogen surges, meaning it shoots up, around day 12 - 13, quadrupling its level but then quickly, within a day, falling almost back to presurge levels.

24 to 36 hours after the estrogen surge, ovulation occurs. The dominant follicle releases an egg and becomes what is called the corpus luteum. In a 28 day cycle, this is around day 14.

The last phase of your cycle is called the luteal phase, referring to the corpus luteum that forms from the dominant follicle. This phase begins after ovulation and is less variable in length, usually lasting 13 - 14 days. Both estrogen and progesterone rise sharply 1 - 2 days after ovulation. They peak about a week later, around day 20 - 22, and then if pregnancy does not occur, they fall precipitously, resulting in low levels by day 28. Now that your hormone levels are low, your next period starts, and it all begins again.

As you can see, there are some hormonal highs and lows throughout the month. And there are several times within the month when your hormone levels are changing rapidly. It should come as no surprise that these changes affect you. For instance, according to Sarah Jio at Woman's Day, when estrogen levels are low during the first week of your cycle, you may have less energy and lower libido. So prepare for that. Plan for extra sleep if you're tired or extra time with your partner if you notice your libido is low.

Menstrual migraines are a classic example of symptoms resulting from the change in hormone levels. According to the Mayo Clinic, estrogen and progesterone may affect brain chemicals associated with headaches. Drops in estrogen, which occur both around the time of ovulation and premenstrually, can worsen headaches. Birth control pills can control headaches by keeping estrogen levels steady.

Although the exact causes are unknown, the Office on Women's Health states that a fundamental cause of PMS is changing hormone levels. Since PMS symptoms can begin anywhere from 1 - 2 weeks before your period starts, consider what is happening with estrogen and progesterone during that time. They are both rising dramatically and then falling precipitously—no wonder some women just don't feel well during that hormonal rollercoaster ride.

"Every woman thinks that it's the sudden drop in estrogen from not ovulating that causes the problems. But in reality, it's the fluctuation of estrogen, along with less progesterone, that is behind many of the typical symptoms of perimenopause," says Steven R. Goldstein, MD, professor of obstetrics and gynecology at NYU Medical Center in New York City.

Having some insight into the complex and elaborate hormonal balance that occurs throughout the month is essential knowledge. It allows you to feel your best with some of life's most vital elements like mood, energy, and libido. And, for any questions about your cycle, feel free to find me or talk to any other certified healthcare professional through OB/GYN Now™, Orchyd's integrated OB/GYN network in the Orchyd app.