Everything You Ever Wanted to Know About Periods
You know it comes every month (usually). You know it has something to do with fluctuating hormones. You know your boobs hurt and you’re craving chocolate. And you know your best friends’ most embarrassing period story (and she knows yours). But what exactly is a period? How does it work, what’s normal, and what’s not normal? Read on for all the details!
It’s a Cycle
At its simplest level, the menstrual cycle is the process by which the body prepares for a potential pregnancy each month. The ovaries produce an egg that could be fertilized and the uterus builds up a fluffy, nutrient- and blood vessel-rich lining that could support a pregnancy. Then, when it turns out the person is not pregnant (which is the case most of the time) the body gets rid of the unfertilized egg and lining through a period, and resets itself to go through the process again the next month.
Understanding the specifics of the cycle, however, can really help in understanding what is normal stuff to experience, what’s not so normal, and how to read clues about what’s going on when things aren’t going smoothly.
First, let’s talk about how we track the menstrual cycle. The first day of your period, which is the first day of regular flow, counts as cycle day #1. The menstrual cycle lasts from this first day of one period to the first day of the next period. The normal range of cycle length is 24-35 days, and it’s a good idea to keep track so you learn what is regular for you. It’s easy to mark the first day of your period on your calendar, or use one of the many apps available for this purpose. A cycle may vary by 1 or 2 days from month to month, but in general we expect it to be pretty consistent. For educational purposes we usually talk about a standardized 28 day cycle, and combined hormonal methods of birth control (like the pill, patch, and ring) are based on a 28 day cycle.
The hormones estrogen and progesterone are the main drivers of your cycle, and they’re helped along by follicle stimulating hormone (FSH) and luteinizing hormone (LH). From a hormone perspective, the menstrual cycle can be divided into two main parts: the follicular phase and the luteal phase. These are on either side of ovulation, which happens right around mid-cycle.
First Half - Follicular Phase
The follicular phase is the first half of the cycle, lasting from the first day of bleeding (cycle day #1) until ovulation (day 14ish). It is named for the ovarian follicle that is produced during this time that contains the egg that will be released this cycle. During your period and the first few days of the cycle, estrogen and progesterone levels are quite low. The pituitary gland in the brain produces FSH, which is the hormone messenger telling the ovary to start growing a follicle, a cyst-like structure in the ovary that contains the developing egg. The follicle is what produces estrogen, and as the egg and follicle mature and grow bigger, they pump out more and more estrogen.
As estrogen surges it stimulates the pituitary gland to surge production of another hormone, LH, and this is what tells the ovary to release the egg. Ovulation occurs when the egg is released. Some people can actually feel this as an ache or sometimes “zing” or sharp “twinge” on one side. The sensation has a name too - mittelschmerz (pronounced “middle-sh-mear-z”) which is german for “middle-pain” or, literally, a pain in the middle of the menstrual cycle.
Second Half - Luteal Phase
Once ovulation occurs, the follicle that was holding the egg gets a new name; it becomes the corpus luteum and is where the term luteal phase comes from. After ovulation, this second half of the menstrual cycle typically occurs on cycle days 14-28. Estrogen and LH levels take a nose dive, and the corpus luteum starts producing the other important hormone of the menstrual cycle: progesterone. There is another small bump in estrogen levels, and together progesterone and estrogen tell the lining of the uterus to grow and mature, preparing for a potential pregnancy.
When there isn't a pregnancy, the lining of the uterus, called the endometrium, only stays stable and intact as long as there is enough progesterone around. As the corpus luteum degrades, progesterone levels start to fall. The drop in progesterone is what triggers the endometrium to start sloughing off, and the bleeding of the next period begins, bringing us back to cycle day #1 of the next cycle.
The average amount of blood lost during one period is about 2 tablespoons, although this varies from person to person. If you find yourself changing completely soaked pads or super tampons every few hours, that’s heavier bleeding than normally expected.
Periods usually last 4-6 days, although any length between 2-7 days is considered within normal range. If your bleeding lasts longer than 7 days you should check in with your sexual health provider.
The follicular phase, when the follicle is developing, can vary in length. Almost all of the difference we see in menstrual cycle length is from the follicular phase. Once ovulation occurs, the corpus luteum has a pretty set schedule. It only lasts 13-14 days very consistently across all menstruating people. So, if you don’t have a 28 day cycle and you want to have a better idea of when you are ovulating, count backwards 14 days from the last day of your cycle. Example: if you have 32 day cycles, where there are 32 days between the first day of one period to the first day of the next, counting backwards 14 days from 32 puts you at 18. This is likely the day you are ovulating, rather than on day 14, which can be useful information, particularly when someone is trying to get pregnant.
This also helps us figure out what’s going on when someone is having irregular periods. Generally, when someone isn’t having periods or is going a long time between periods, they aren’t ovulating, and we look for underlying issues that could be preventing regular ovulation. Polycystic Ovarian Syndrome (PCOS), pituitary tumors, and hypothyroidism are all conditions that can interrupt regular ovulation. If you realize you’re going three months or longer between periods, and you're not on any hormonal birth control, it is definitely time to see your healthcare provider.
Caveat to the above: if someone is on hormonal birth control, it is totally fine to not have a period. Often for folx who have super heavy or super painful periods, or have irregular periods due to PCOS, the best way to manage these symptoms is to use hormonal birth control to stop their monthly period.
When It's OK to NOT Have a Period
"Uh, hold on a second" you may be thinking, "Isn't it important for your body to have a period; it has to clean itself and get rid of all that stuff that comes out during a period, right?"
Well, yes, sorta, but also, no.
Hormonal birth control does 3 major things to prevent pregnancy:
The "keeping the uterine lining thin" thing is extra important for another reason: protection against cancer. When someone is not on hormonal birth control, and they are not having regular periods, there is a concern that the uterine lining isn't shedding, and is thicker rather than thin. The cells on the inside of the uterus that make the endometrial lining are working overtime to divide and divide and keep that lining thick - they're not getting a hormonal message to let the lining go and to re-set. In the short term (months) this can lead to an "unstable endometrium" and unpredictable heavy or prolonged bleeding. In the long term (years) this can lead to cellular changes in the endometrium called "endometrial hyperplasia" (pre-cancer) or even endometrial cancer.
So, yes, when someone is not on hormonal birth control, they do "need to have a period" to shed the endometrial lining.
When someone is on hormonal birth control, however, the endometrial lining is super thin. There just isn't anything that needs to come out. Scientific evidence that supports this shows that people who use hormonal birth control have a significantly decreased risk for endometrial cancer. We don't know exactly why this is, but one hypothesis is that the thinner endometrial lining is undergoing fewer cell divisions over its lifetime (makes sense; that's why the lining is thin). And, one thing we do know is fewer cell divisions = fewer opportunities for DNA to get copied incorrectly (mutations) = fewer opportunities for cancer to develop.
That hypothesis also applies to the observation that hormonal birth control users have a significantly lower rate of ovarian cancer too. Remember, the other way hormonal birth control prevents pregnancy is to stop ovulation. The whole process of maturing an egg and releasing it involves a bunch of cell division inside an ovary. Fewer lifetime ovulation events = fewer cell divisions = fewer opportunities for DNA to get copied incorrectly (mutations) = fewer opportunities for cancer to develop.
Guess what else decreases ovulation events and endometrial lining turnover? Pregnancy. Guess what else is significantly associated with decreased rates of endometrial and ovarian cancer? Pregnancy. And, it seems that the risk decreases further with each pregnancy, similar to the observation that protection from endometrial and ovarian cancer seems to last longer the longer hormonal birth control is used. Also, colorectal cancer. Hormonal birth control use and pregnancy are associated with lower rates of colorectal cancer.
So, when someone is on hormonal birth control, no, they totally do not need to have a period. Also, surprise! You thought birth control was just to make your periods better and to prevent pregnancy, but it turns out you're also reducing your risk for some types of cancer. Go you!
Need to check in with a period expert? That’s totally my job! Come see me, I’m really good at having conversations about periods and birth control in a non-awkward way.
©2017 Chelsea Gould