If you were lucky enough to attend a middle or high school sex ed class that delved further into menstruation than a cursory glance, you may know about the important role your hormones play in your menstrual cycle. If you’re like the majority of Americans, you may have never had a deeper look into monthly hormonal fluctuations and all the ways they can affect your body, your mind, and your mood. Whether you’ve known the biological reason you get cramps and crave chocolate chip cookie dough (straight from the fridge, thank you) or not, understanding menstrual cycle hormones can help you become more aware of your body and your fertility.

Your Menstrual Cycle 

Before we talk about all of the different hormones that are play during your menstrual cycle, let’s talk about your cycle overall. Throughout each month, the pituitary gland in your brain is communicating with your ovaries. If, during ovulation, your egg is fertilized and implants properly into your uterus, you’ll see a pink plus sign on a pregnancy test. If your egg is not fertilized, your uterus will shed its lining and you’ll get your period.

The number of days in your cycle is measured by counting from the first day of one period to the first day of the next. On average, cycles are 28 days long but can range from 21 days (a shorter cycle) to 35 days (a longer cycle). This, of course, only applies to women with an average cycle — there are a lot of variables to take into account and many women have even shorter or longer cycles, both indicating that you may not be ovulating or ovulating regularly. If this is the case, you should see your doctor.

The average menstrual cycle lasts between 5 and 7 days but, again, can be longer or shorter. If you’re bleeding for more than 7 days, it’s possible that you are not ovulating.

Understanding the Role of Each Hormone

There are three main hormones that affect your menstrual cycle. These are estrogen, testosterone, and progesterone. Here’s an overview of each:

Estrogen

Your ovaries are the main source of estrogen in your body, though, your adrenal gland produces some, too. Your entire body uses estrogen in different ways and it plays a key role in controlling the menstrual cycle and becoming pregnant.

Testosterone

Women tend to have lower levels of testosterone than men do but it is still present and contributes to the menstrual cycle, sex drive, and overall sense of well-being.

Progesterone

The main role of progesterone is to control the build-up of your uterine lining, helping to maintain it if you become pregnant. If you don’t become pregnant, your progesterone levels dip, your lining sheds, and you get your period.

Your Menstrual Cycle Hormones, By Phase

Now that we’ve gone over the basics — what a menstrual cycle is, what an average cycle looks like, and which hormones are dominating your cycle — let’s dive into a week-by-week look at how your hormones work each month. Keep in mind that the “days” given are based on an average menstrual cycle and yours may differ.

Menstrual Phase (Days 1 – 7) — Rising Estrogen

On the first day of your period, your estrogen levels are at their lowest all month. This entire week they begin to climb and can make you feel more social and optimistic. This is why it’s not uncommon to feel terrible right before your period and happier and less stressed once you actually start bleeding. Progesterone and testosterone are both laying low during the first week of your cycle but they are still there, behind the scenes.

Follicular and Ovulatory Phases (Days 1 – 14) — Rising Estrogen and Testosterone

Your progesterone levels are still taking it easy but estrogen and testosterone are both rising during your follicular phase. Let’s back up, though. Your follicular phase starts on the same day as your period begins but lasts until ovulation begins (on average, around day 14 of a 28-day cycle).

During ovulation, your brain signals to your ovaries to begin growing eggs, one of which will mature in a follicle. Your uterus is simultaneously growing a new endometrium (or uterine lining). Due to peaking estrogen levels, your brain signals a surge of Luteinizing Hormone (LH) and follicle-stimulating hormone (FSH) which send your matured egg into your fallopian tube to await fertilization.

Emotionally, you’re likely to feel more confident and daring, thanks to this estrogen-testosterone power combination. You also have a higher pain tolerance during this phase, so if you must get a bikini wax, do it now.

Luteal Phase (Days 15 – 28) — Rising Progesterone; Declining Testosterone, and An Estrogen Rollercoaster

Immediately after ovulation, you begin the luteal phase of your menstrual cycle. This lasts until the day before you get your next period (unless you become pregnant). The egg you released into your fallopian tube during ovulation stays there for 24 hours. If it isn’t fertilized by sperm at that time, it disintegrates and triggers the shedding of your uterine lining by using up any remaining progesterone. If it is fertilized, it will implant into your uterus where progesterone will continue to keep the endometrium lining healthy to support a pregnancy.

So many things happen during the luteal phase. To understand the hormones better, let’s break it in half.

The first half of your luteal phase may feel a bit like a less severe version of PMS. This, too, can be blamed on plummeting levels of estrogen (the second dip you’ll experience in each cycle). During this time, your progesterone levels are climbing, making you feel more introspective and cautious, while your testosterone takes a nosedive.

The second half of your luteal phase brings your estrogen levels back up (told you it was a rollercoaster this week!) while your progesterone continues to rise. By now, you shouldn’t be having any PMS symptoms.

Now, your cycle starts all over again, providing that you aren’t pregnant. If you are, you can look forward to 9 months without a period. Understanding how hormones work during your menstrual cycle can actually make managing your fertility easier. The more you know about how your body works, the easier it is to notice fluctuations that could be affecting your menstrual cycle.

Menstrual Cycle Hormones and Fertility

In reproduction, there are a number of hormones that regulate cycles of egg production, ovulation, and menstruation. If these chemicals drift out of balance, it can be difficult to get pregnant. If this happens, you may ultimately need to talk to a doctor about the following examples of fertility-related hormones.

(Also read: Male Hormones and Fertility–What You Need to Know)

  • Gonadotropin-releasing Hormone

    (GnRH) is produced in the hypothalamus. It then travels to the pituitary gland and stimulates the secretion of two other hormones, LH and FSH. GnRH is produced in pulses, and the frequency of these pulses determines whether LH or FSH is released. The pulses of GnRH speed up or slow down at different times during the reproductive cycle.

  • Luteinizing Hormone

    (LH) helps regulate a woman’s menstrual cycle. An increase in LH levels triggers ovulation after a follicle has fully matured. Measuring LH levels is a common way to track ovulation. A surge in LH levels typically lasts 24-48 hours and indicates that the mature egg has been released and is ready for fertilization.

  • Follicle-Stimulating Hormone

    (FSH), as the name suggests, is responsible for the development of follicles in the ovaries, the areas where individual egg cells mature before ovulation. Typical levels for a woman of reproductive age are between 4.7 and 21.5 mIU (milli-International Units)/ml.

Effects of Hormones on Fertility

Working together, these hormones determine the course of the entire reproductive cycle:

  • Low-frequency pulses of GnRH tell the pituitary gland to produce FSH, which causes the follicle to develop.
  • As the follicle reaches maturity, estrogen levels eventually reach a tipping point. This causes the hypothalamus to increase the frequency of GnRH pulses.
  • This signals the pituitary gland to start producing LH instead, triggering ovulation.
  • Meanwhile, the follicle – now emptied of its egg – develops into the corpus luteum. In turn, this produces progesterone, signaling the uterine lining to prepare for the egg after fertilization.

If levels of any of these hormones are too low or too high, the cycles of menstruation and ovulation can be thrown off, causing fertility problems. Hormone imbalances can be caused by a number of diseases or disorders, including Polycystic Ovary Syndrome, diabetes, drugs including antidepressants, and even stress.

Your doctor may recommend blood tests if they suspect a hormone imbalance is affecting your fertility. Hormone imbalance can be treated with drugs or injections of hormones, or your doctor could try to treat the underlying issue that is causing the imbalance.

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