When we hear the term “menstrual cycle,” we usually go right to thinking about our period. Periods are just one of many steps in the cycle though, and ultimately your period is just a symptom of what your hormones are doing!
What are hormones though, and why should we care about them? What is our period actually telling us, and how do hormones matter both for health and if we’re trying to conceive? Keep reading to learn all about the hormones that drive the menstrual cycle and ultimately contribute to your overall health!
What are hormones?
Hormones are chemicals that occur naturally in your body and travel between organs to send messages and coordinate body processes. While we call all of these chemical messengers hormones, they can be different types of chemicals and they regulate many different systems.
For instance, some hormones (including estrogen and progesterone) are made from fats like cholesterol, and some hormones are actually protein-based! And there are hormones involved in your stress regulation, growth, metabolism, and of course, your reproductive system.
Today, we’ll focus on the four main hormones that drive what’s going on in your menstrual cycle (although there are certainly more). We’ll discuss what each hormone does and when it occurs during the cycle, since they all have their particular time to shine.
What are the main menstrual cycle hormones?
1. Follicle Stimulating Hormone
Let’s start at the beginning of the menstrual cycle! Your period begins on cycle day 1 and hormonal activity is low overall, but a few days after that, follicle stimulating hormone (FSH) appears. The first half of your cycle is called the follicular phase for this reason!
FSH is released from the brain, and travels down to the ovaries to trigger the development of several follicles. Follicles are small fluid-filled sacs in the ovaries that contain immature eggs, and once FSH begins to act on the ovaries, several follicles start to mature.
FSH levels tend to change throughout your lifetime. Initially, FSH levels are usually relatively low. As you age and your ovarian reserve (or the number of eggs left to mature) diminishes, your ovaries have to work harder and it takes more FSH to stimulate follicles.
This can be perfectly normal as menopause approaches, and in fact, high FSH is a sign of the time before menopause, called perimenopause. If you’re on the younger side though (in fertility terms, that’s under 35) high FSH can indicate premature ovarian insufficiency and make it more challenging for you to conceive.
When several follicles begin developing, the ovary responds by sending a hormone of its own back to the brain–estrogen. Estrogen tells the brain that fertility is rising, and triggers a number of other symptoms. This is approximately the start of the fertile window, or the time during which you can actually get pregnant.
Estrogen also acts on the cervix, causing your cervical mucus to become more fluid to allow sperm transport. While this particular impact of estrogen is sometimes overlooked, it’s actually crucial if you’re TTC! Sperm can’t make it all the way to the egg without some help, and fertile cervical mucus does just that.
Estrogen reaches its highest point just before ovulation (when the egg is released from the ovary), and it’s responsible for increased energy levels, swollen breasts, and thickening of the uterine lining (so how heavy your period is can be related to your estrogen levels).
While high estrogen is helpful when you’re TTC, especially right before ovulation, it is possible to have estrogen that is too high, or out of balance with the rest of your hormones. This is called estrogen dominance.
3. Luteinizing Hormone
At this point in the cycle, you still haven’t ovulated yet. That’s where luteinizing hormone (LH) comes in! After several days of estrogen rising, one follicle will become dominant over the others, and this follicle will prepare to release an egg.
The release of the egg, termed “ovulation,” comes only after the signal from the brain, though. This signal is LH, and it does two things: it causes the egg to be released, and it turns the leftover follicle into the corpus luteum, a tiny brand-new organ that produces progesterone.
The day you get a positive LH test is usually the day your chances of conceiving are the highest!
Once LH triggers ovulation, the cycle isn’t over though–in fact, there’s an entire half of it left! The second half of your cycle is called the luteal phase (because of the role of the corpus luteum), and this phase is almost entirely dominated by a single, crucial hormone: progesterone.
As soon as the egg is released, the corpus luteum begins producing progesterone in increasing amounts. Progesterone levels rise for several days and then peak between days 7-10 after ovulation, known as the implantation window.
The implantation window is the time during which a fertilized egg could implant in the uterine lining, and it’s critical because if a fertilized egg has nowhere to go, pregnancy will never occur! During the implantation window, it’s progesterone that stabilizes the uterine lining and keeps it from shedding so that implantation has a chance.
If progesterone is too low, the uterine lining may not hold during the entire implantation window, and your period may come early. This is why progesterone levels during early pregnancy are important to prevent miscarriage.
If the corpus luteum is formed properly and progesterone levels rise high enough, then we consider that ovulation to have been successful! Successful ovulation is important for conception, mood, and good sleep, among other things.
That’s why it’s important not only to predict ovulation with LH and estrogen, but also to confirm successful ovulation with progesterone.
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