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Why Is My Menstrual Cycle Getting Shorter? 8 Possible Reasons

February 17, 2022
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Whether you love it, hate it, or feel decidedly neutral about it, a menstrual cycle is simply part of life. But when it comes to menstrual cycles, there's really no such thing as "normal"—everyone is unique, and only you know what falls into the realm of "regular" for you. 

Still, if you've had consistent periods in the past, it can be jarring when your cycle suddenly becomes shorter than your usual—and even stranger when it stays that way. But why do menstrual cycles and periods get shorter, and what can it indicate about your overall health? Here's what you need to know. 

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Reasons your menstrual phase may get shorter.

Your menstrual phase, aka the time in your cycle when you have bleeding, can last anywhere from two to seven days, according to the American College of Obstetricians and Gynecologists1 (ACOG). If the length of your period falls anywhere on that spectrum, doctors will usually consider it "normal." That said, you know what's typical for you and what's not. There could be a few reasons why the menstrual phase of your cycle is suddenly shorter, including:

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You're exercising a lot.

Under most circumstances, "exercise does not affect the menstrual cycle in any significant way," says Jennifer Lew, M.D., an OB/GYN at Northwestern Medicine Kishwaukee Hospital. But exercising at extreme or high competition levels (think marathon training) can interrupt your cycle, leading to shorter periods or no periods at all, she says. This specifically affects your hypothalamic-pituitary axis, she says, which is the hormone feedback system that involves your brain and ovaries. 

"The hypothalamus controls your cycle," explains Christine Greves, M.D., a board-certified OB/GYN at the Winnie Palmer Hospital for Women and Babies. "If you're exercising at a very intense level, your body may detect that it's not a good time for you to be reproducing and interfere with your ovulation."

As a result, "you may be building up a uterine lining but not getting the signal to shed it from lack of conception," says functional medicine gynecologist Wendie Trubow, M.D., MBA.

What's more, she adds, "if a woman is exercising enough to disrupt her ovulation, then she may be also suppressing her estrogen levels, which can lead to shorter periods since a woman doesn't build up enough of the uterine lining and so, less sheds and shorter menstruation."


Your stress levels are high.

Research has repeatedly linked stress to irregular menstrual cycles, although it seems to be different for everyone. One study published in the Journal of Clinical & Diagnostic Research2 found a mixed bag with cycle length in undergraduate students who reported having higher levels of stress.

However, an older study3 found that women who work in stressful jobs are twice as likely to have short periods as those who work in jobs that aren't considered stressful. "Extreme stress can affect cycles by interrupting ovulation or delaying ovulation," Lew says.  

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You're breastfeeding.

It can take weeks or even months for your period to start again after you have a baby, Greves says. But there's a wide range for everyone, and breastfeeding can play a role, too. "Breastfeeding impacts your hormones and ovulation—your hormones are not completely back to normal during this time," Greves says. The hormone prolactin tells the glands in your breasts to make milk, but it can also lead to shorter and lighter periods or suppress them entirely, she says. 


You're taking new medication.

There are several medications that have the potential to shorten your period, Greves says. She lists hormonal birth control pills, hormonal IUDs, thyroid medications, antidepressants, and medications to treat epilepsy as possible causes. This won't happen to everyone, though. "A lot depends on how your body responds to the medication," she says. 

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You're in perimenopause.

Perimenopause is a term used to describe the years leading up to menopause. When you're in your forties, your ovaries start to slow their production of estrogen, Greves says.

This can cause your periods to get shorter and lighter, the ACOG4 explains, although some women may have heavier periods—it really depends on your body. Your periods may also start to come further apart, according to Lew.

Reasons why your cycle overall may get shorter.

Your menstrual cycle is actually made up of four phases. There's your menstrual phase, which is the time of the month when you bleed; the follicular phase, which is when your pituitary gland releases a hormone called follicle-stimulating hormone (FSH) that causes the egg-containing follicles in your ovaries to mature; the ovulatory phase, which is when an egg is released from a follicle in your ovary; and the luteal phase, where estrogen and testosterone start to drop in your body, while levels of the hormone progesterone rise.  

A typical cycle can be anywhere from 21 to 45 days, according to the ACOG1. But, again, you know what's normal for you. 

The biggest reason you might notice your cycle getting shorter is poor ovulation, says Mary Jane Minkin, M.D., a clinical professor of obstetrics and gynecology and reproductive sciences at Yale Medical School. "When we ovulate—around mid-cycle in general—the ovary turns the area from which we ovulated, the follicle, into a producer of progesterone," she says. "Progesterone turns the lining of the uterus into an area where a fertilized egg would like to implant." 

If there's no fertilized egg, the follicle that's making progesterone dies, she says. Then, the progesterone levels fall and you have your period. "Anything that leads to poor ovulation will lead to less progesterone, and you will get your period sooner," Minkin says. 

Just like with shorter periods, this can happen with age, after you have a baby, and when you're breastfeeding, Minkin says. 

"If you get one short cycle, I would ignore it—no evaluation is necessary," Minkin says. "But if it keeps on happening, a check-in with your gynecologic provider may be worthwhile."

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Is there such a thing as a "normal" period?

For the record, no, there is no such thing as a normal period. "It's only what's normal for you," Greves says. "We are all different."

However, Lew points out that there is a range of what's considered normal in medical terms—namely, cycles of every three to six weeks, with a period that lasts two to seven days. If your cycle is outside of this range or has suddenly fallen outside of it, she recommends checking in with your doctor about a possible evaluation.

Bottom line.

There are a slew of possible reasons why you might develop a shorter period or shorter menstrual cycle. If you notice that things have changed for you and they're consistent, it doesn't hurt to check in with your doctor to see what could be behind all of this.