Welcome to Day 4 of The Science of Your Cycle, Groove’s amazing (and 100 percent FREE) 7-day mini-course that will teach you everything you need to know about how your body (and your period) works. If you thought the first half of the menstrual cycle was cool, just wait until you watch today’s video! Today, we’re going to cover how ovulation happens, why a pregnancy is super unlikely during certain parts of the menstrual cycle, and what makes super accurate period predictions possible (even if you have irregular cycles). By the end of this video, you’ll have a better understanding of how periods work than most medical professionals.
What was the most surprising thing you learned in today’s video? We’d love to hear your thoughts in the comments below!
00:00 - Welcome back to The SCIENCE of Your Cycle, Groove’s amazing and FREE 7-day course all about the awesomeness of the menstrual cycle. Today is Day 4. Yesterday was part 1 of Getting to Know Your Cycle, and today is part 2.
00:28 - Today’s goals are to learn how your hormones work together to create the changes that happened during the last two phases of the menstrual cycle, to gain an understanding of how ovulation occurs, to learn what purpose progesterone serves during your cycle, and lastly to understand why a pregnancy isn’t possible after ovulation.
00:55 - First up, let’s do a quick recap of everything that we learned yesterday when we went over the first two phases of the menstrual cycle. Menstruation is the shedding of the uterine lining. The vagina’s default mode is to be an acidic sperm-killing machine,which is pretty awesome if you ask me. Growing follicles make estrogen, and that estrogen triggers the production of cervical fluid. Cervical fluid becomes increasingly wet and slippery before ovulation, which allows sperm to survive and reach the egg. And lastly, the length of the follicular phase or can be influenced by many environmental factors like stress, exercise, diet, sleep changes, illness, etc. The follicular phase for people with PCOS is the phase that you can blame — that’s the one that has variability, and we’ll discuss that in a little more detail today.
01:56 - You saw this last time, but we’re going to go over it again. The four phases of the menstrual cycle are menstruation, the follicular phase, ovulation, and the luteal phase. We went over menstruation and the follicular phase yesterday, and you’re a total pro at those by now…I’m certain of it. Today, we’re going to cover ovulation and the luteal phase.
02:26 - First up, let’s discuss ovulation. Ovulation is part of the ovarian cycle, and if you remember from yesterday, the ovarian cycle is all of the changes that occur in the ovaries during a single menstrual cycle. Ovulation is the release of a mature egg from one of the ovaries, and to be more specific, it’s the release of a mature egg from one of the follicles (which is an egg sac that develops in the ovaries). Ovulation can happen anywhere from about 9 to 25 days after the first day of your period. If you have a regular cycle, and I mentioned this before, but for someone with PCOS or amenorrhea, you might go months between the first day of your period and ovulation. So that’s where the variability in your cycles is. And then lastly, ovulation is triggered by a sudden increase of luteinizing hormone, which remember is made by the pituitary gland in the brain.
03:35 - What happens during ovulation is that first, a follicle’s estrogen crosses a threshold. Second, the pituitary gland releases an LH, or luteinizing hormone, surge. And third, the follicle releases its egg. Now we’re going to discuss each one of those in more detail.
03:56 - One: the first thing that happens to follicles is that estrogen crosses a threshold. We talked about this a few times already, but the bigger the growing follicles get, the more estrogen they make. At some point, one of those growing follicles is going to produce so much estrogen that it’s going to cross the threshold. Currently, that specific threshold is unknown to the medical community — they’re not exactly sure where that threshold is and they’re still studying it. But when one the follicle’s estrogen production is high enough, it crosses the threshold and that’s basically your follicle’s way of saying “Hey there, this is inside me…see it right there? Yeah, it’s ready to ovulate!”
04:46 - Secondly, the pituitary gland releases a luteinizing hormone surge. I said already that one of the follicle’s estrogen production will eventually get so high that it crosses the threshold, and once it crosses that threshold, the mature follicle’s high estrogen production triggers the pituitary gland to produce a sudden surge of luteinizing hormone. That follicle produces tons of estrogen, which is basically saying “Hey, this egg is ready to come out!” and then your pituitary gland responds by producing a sudden surge of luteinizing hormone. Number three: the follicle releases its egg. This high estrogen production by one of by the mature follicles triggers the pituitary gland to produce a sudden surge of luteinizing hormone. That sudden surge of luteinizing hormone is basically your pituitary gland’s way of saying “Hey follicle…yeah you — the one down in the ovary with the egg that’s ready to ovulate. Go ahead and release that egg!”
05:24 - Next up, your mature follicle that’s ready to release an egg responds to this surge of luteinizing hormone that’s made by the pituitary gland by releasing its egg. And that release of the egg is ovulation. Lastly, it’s important to note that an ovulated egg will die within 24 hours if it isn’t fertilized by a sperm, and that’s really important to understand and really interesting. It’s not something that many of us are taught. The takeaway from this is that one maturing follicle makes enough estrogen to trigger the pituitary gland to produce a sudden surge of luteinizing hormone, and then this luteinizing hormone triggers the mature follicle to ovulate it’s egg.
06:55 - Now we’re going to do an overview of the luteal phase, which is the last phase of the menstrual cycle. The luteal phase is actually part of the ovarian cycle, which are the changes that occur in the ovaries during a single cycle. But the luteal phase affects what happens during the uterine cycle. So it’s part of the ovarian cycle, but it directly affects the uterine cycle. The luteal phase is the time between ovulation and the first day of your next period. Once you ovulate, count the number of days between then and when your next period starts and that’s the luteal phase. It typically lasts between 11 and 16 days, even if your cycles are irregular. Remember earlier I mentioned that the follicular phase is a phase that has all of that variability? So if you have PCOS, the follicular phase is to blame — it’s not the luteal phase. So once ovulation occurs, even if your cycles are irregular, even if you have PCOS, if your body does manage to ovulate then you’re going to have between 11 and 16 days before your next period starts. That’s not going to change. Next up, the luteal phase is dominated by the sex hormone progesterone. The final thing that happens is that the lining of the uterus prepares itself for potential pregnancy.
08:36 - Here’s what happens during the luteal phase, and then we’re going to go over each one of these points in more detail. Number one: the empty follicle becomes the corpus luteum. Number two: the corpus luteum makes progesterone. Number three: progesterone affects the body. Number four: the corpus luteum dies.
08:56 - Number one: the empty follicle becomes the corpus luteum. Remember that surge of luteinizing hormone that was made by the pituitary gland that triggers ovulation? Well, this surge of luteinizing hormone also serves another purpose. After a follicle releases an egg during ovulation, the surge of luteinizing hormone actually causes the newly empty follicle to undergo a process called luteinization, and luteinization is where this hormone gets its name.
10:04 - So the newly empty follicle undergoes a process called luteinization because of this LH surge, which transforms this newly empty follicle into a structure that’s called the corpus luteum, which in Latin means yellow body. The corpus luteum actually makes the sex hormone progesterone for the next 11 to 16 days. And it’s by no coincidence that the length of the luteal phase is between 11 and 16 days.
10:34 - Next up, progesterone affects the body. The corpus luteum makes progesterone for 11 to 16 days. Progesterone weakens the lining of the uterus to prepare it for a potential pregnancy. Progesterone counters estrogen’s effects and dries up cervical fluid. Remember, estrogen triggers the cervix to make cervical fluid to keep sperm alive. Progesterone counter the effects and makes cervical fluid dry up, and sperm can no longer survive in reproductive tract. Progesterone also stops follicle development, which prevents another ovulation from happening. So after you ovulate, you’re not going to ovulate again until during your next menstrual cycle. And then lastly, progesterone heats up the body, making the body’s resting temperature noticeably higher after ovulation…we’re going to go into that one in a little more detail in the coming days. A takeaway from that: progesterone, which is made by the follicle that ovulated it’s egg, thickens the lining of the uterus, dries up cervical fluid, prevents another ovulation, and also heats up the body.
12:05 - The fourth step in this process of the luteal phase is that the corpus luteum dies. I mentioned already that the corpus luteum makes progesterone for between 11 and 16 days, and even if your cycles are irregular, your luteal phase is going to be 11 to 16 days long. So even if your cycles are irregular, the corpus luteum (or yellow body) is going to make progesterone for between 11 and 16 days if the egg was not fertilized within 24 hours of ovulation (aka the egg dies). The corpus luteum dies after those 11 to 16 days. Remember I said an egg would die within 24 hours after ovulation if it’s not fertilized by a sperm? If the egg is not fertilized, the corpus luteum will die after 11 to 16 days. Or if the egg was fertilized but for some reason was not able to successfully implant itself into the wall of the uterus — which is where it would have grown and been housed during pregnancy — the corpus luteum again will die after 11 to 16 days. And if the corpus luteum dies, obviously it can’t make progesterone anymore. So if the corpus luteum dies, progesterone levels plummet and the uterine wall breaks down, which means you start your period. The takeaway from this: progesterone prevents another ovulation, heats up the body, and dries up cervical fluid — but it only does those things if ovulation has already happened.
13:46 - Here’s a quick summary of the menstrual cycle that we’ve learned over the past two days. Then we’ll be done — I know this is a long one, but we’re almost done so bear with me. The menstrual cycle: you start your period; then follicle stimulating hormone causes mature follicles to grow and develop and those follicles produce increasing amount of estrogen as they grow; estrogen that is made by the follicles triggers the cervix to make cervical fluid, and that cervical fluid becomes increasingly wet and slippery as ovulation approaches; cervical fluid then allows sperm to survive in the female reproductive tract for up to 5 days waiting to fertilize an egg; then ovulation occurs when a mature follicle triggers a surge of luteinizing hormone; it’s estrogen levels cross the threshold, and it triggers the pituitary gland to make a surge of luteinizing hormone; and luteinizing hormone transforms the newly empty corpus luteum (or yellow body in Latin); the corpus luteum (or yellow body) makes progesterone for 11 to 16 days; progesterone dries up cervical fluid, prevents another ovulation, thickens the wall of the uterus, and heats up the body; and if a pregnancy does not occur for whatever reason, the corpus luteum will die after 11 to 16 days — its progesterone production will stop (meaning progesterone levels drop), and then the uterine wall breaks down because of that and your period starts.
15:45 - Here are a few visual representations of what happens during the menstrual cycle. The one on the left is just a basic diagram. The one on the right side in green shows estrogen change throughout the cycle. I you can imagine that the left side of it is when your period starts, and then on the right side at the very end of that chart is going to be the day before your next period starts. So you can see the second box down is the ovarian cycle, and everything highlighted in green is the follicular phase. The follicles are growing and developing, and you can see that as we get further to the right, the estrogen level rises, and that represents the follicles making increasing amounts of estrogen. And then cervical fluid responds to estrogen and those growing follicles by becoming increasingly wet and slippery. It starts off sticky and tacky — it might have progressed to a little creamy or milky.
16:55 - On the left here we have ovulation — so, again, the green represents the rising estrogen levels. The next one down in the ovarian cycle, we have the follicle releasing an egg and we have cervical fluid at its peak, which is very wet and slippery. Then the last chart on the right signifies the luteal phase — so we have the progesterone. You can see the production is very high as you get to the right. Again, that’s towards the end of the cycle. The progesterone is very high in the last phase of the cycle. The follicle, which is empty, produces progesterone and then slowly shrivels up and dies. And then cervical fluid — because that progesterone — goes from wet and slippery too very sticky again, and then eventually dries out.
17:54 - I know that was a lot of information today, but tomorrow things are going to get super awesome. You’re going to learn how tracking your menstrual cycles can actually benefit your life, and you’ll also learn how to apply all of the knowledge that you’ve learned within the last few days to predict your next period with extreme accuracy. And lastly, you learn about some of the very unexpected but super super amazing benefits that you’ll glean from tracking your menstrual cycles. I cannot wait for all that information — it’s going to be super amazing. I know we’ve covered a ton of information over the last two days, and you should be super proud of everything that you just learned, because that’s more than most people will ever understand about the menstrual cycle. I’m hoping to change all that.
18:25 - You should feel like this Queen Bey right now because you deserve it. You should feel super proud of yourself. I’m so excited about what we’re going to cover tomorrow, and I will see you then!