Irregular Periods Explained: The Most Common Reasons Your Period Is MIA
A missed period sucks. First, many of us start to get anxious that we might be pregnant. Next, we have no way of predicting when it might decide to arrive, leaving us vulnerable to bleeding all over the place at a moment's notice. And then there is the other looming question: What made us miss it in the first place?
For people with periods, paying close attention to our cycles helps us stay in tune with what our body is trying to communicate. A missed period can be a signal that something else is going on with our body that we need to look into. It can be worth doing a mental self-check about any changes you've experienced lately and talking to a doctor about.
A normal period versus an irregular period
"The monthly menstrual cycle typically occurs every 28 days, is controlled by various hormones and is a key function of the female body," says Dr. Sherry Ross, MD, OB/GYN and Women’s Health Expert at Providence Saint John’s Health Center in Santa Monica, California. "Your 'period' begins around 11-12 years of age, lasts 2-7 days and continues until your reach menopause, which occurs around 51 years old."
Ross continues: "Ovulation is an important part of the menstrual cycle and occurs around Day 14 when an ovarian follicle produces an egg, which can be fertilized by sperm. The egg is only available to be fertilized for 24 hours before it disintegrates. Once you have ovulated, your period will occur, which is typically 14 days later."
The amount of blood shed during a period varies from person to person. Some people who menstruate routinely have heavier periods (losing up to 12 teaspoons of blood each month) while others may experience a period that's almost non-existent (losing as little as four teaspoons of blood).
If you've been menstruating for a while, your body will get into a period flow, which is why an irregular period is usually defined as any type of bleeding that's abnormal when compared to your last few menstrual cycles. It can include everything from a late period to early bleeding, and scant bleeding to extremely heaving bleeding. For many individuals, this can even mean an absent period (amenorrhea) or two periods in one month (metrorrhagia). Two periods in one month, or a period every two weeks, are thought to be caused by an imbalance in estrogen and progesterone and may require a trip to the doctor since this can induce anemia.
And if you're not prone to PMS, you can also consider a period irregular if you experience heavy cramping and bloating or headaches.
The many causes of irregular periods
Every person who menstruates will experience an irregular period from time-to-time, and though, in most cases, they aren't dangerous, it's important to figure out what's causing the irregularity. Here are a few common reasons you may be experiencing an abnormal flow.
Stress is the most common cause of irregular periods. Cortisol, the stress hormone, has a direct impact on how much estrogen and progesterone, two sex hormones, gets produced by the body. If you have too much cortisol in your bloodstream, the time and flow of your cycle could change.
Dr. Carolyn C. Thompson, MD, FACOG, board-certified OB/GYN, explains that in order for a woman to have a normal menstrual cycle (in which she does not become pregnant), the hypothalamus in the brain must send hormonal signals to the pituitary gland, which must in turn signal the ovary, which then signals the uterus.
In case you need an anatomy refresher, the hypothalamus is adjacent to areas in the brain that influence emotion; neurotransmitters form these centers can shut down the signals to the hypothalamus and therefore stop the outgoing signals from the hypothalamus.
"Evolutionarily speaking, this makes sense — if a woman is under a great deal of stress, either physical or emotional, it is likely not an ideal time for a pregnancy, so the system shuts down," Thompson adds.
Another common reason for a late or missing period is the food you eat and, more specifically, the weight you're carrying. If you're eating a diet that's rich in unhealthy carbs or if you've gained weight, your body will produce varying levels of certain hormones, shifting when you ovulate.
The same goes for people who menstruate as they lose weight. "In order for a woman to maintain a regular cycle, her body fat percentage needs to be at least 17-22 percent. This is again related to the evolutionary idea that a state of starvation is not conducive to maintaining a healthy pregnancy, so, again, the system shuts down," says Thompson.
Our bodies need energy to menstruate. If you're burning too much of your energy in the gym, there will be nothing left for your body to use during that time of the month.
"The list of what causes irregular periods is longer than you think, but we know excessive exercising, sudden weight changes and being underweight can offset your hormone levels. One of these hormones is called Leptin and is produced in fatty tissue. Excessive exercising and drastic weight changes can decrease the body fat, causing this and other hormones to drop, contributing to irregular periods," says Ross.
4. Birth control pills
It can take several months for your body to get used to the dose of hormones birth control pills deliver. On top of that, Ross explains that one of the side effects of a low dose birth control pill is a light or non-existent period.
For some, this is a welcomed side effect. When a menstruating person stops taking the pill, their periods may take one to three months to return to normal.
"The birth control pill doesn’t cause you to have amenorrhea," Ross says. "It may be once you are off the pill you may find you have an underlying hormonal problem that was masked by taking the birth control pill. If this is the case, you should alert your healthcare provider."
Next Up: Polycystic ovary syndrome (PCOS)
Originally published January 2016. Updated June 2017.