Why Is My Period Suddenly Shorter? OB-GYNs Explain the Possible Reasons

Several clean white menstrual pads on orange background

I’ve never been the biggest monthly bleeder, which is something I’ve always been quite grateful for. For decades, my periods lasted just a few days, and I never required any sort of “super” assistance. A few years ago, though, after I turned forty, I noticed that they started getting shorter than before.

It wasn’t until I finished a box of 16 tampons and realized I’d purchased it an entire year prior that it hit me just how much my periods had tapered off. I stopped using tampons entirely, opting instead for period underwear, which holds the equivalent of one to two tampons. For the past two years, though my period continues to come on time every four weeks, I bleed for just a day or two.

Curious about why my period has been gradually drifting off into the sunset, I reached out to two OBGYNs to learn more about why periods may shorten in duration. It turns out that there are many different reasons, and while the reason for mine seems pretty straightforward, you may be surprised by all the factors that can impact the duration of your menstrual cycle. Ahead, learn about the varied reasons why your period may be shorter than in the past.


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Stress, especially when it goes on for long enough to be considered a chronic issue, can upend our lives in countless ways, and our periods are one of them. “Stress can disrupt the hormonal balance in the body, leading to shorter menstrual periods,” says board-certified OB-GYN Stephanie Hack, MD/MPH, FACOG. Excess stress creates an abundance of cortisol in our bodies, and that can disturb and disrupt how well our other hormones function.

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I’m pretty sure that this is the reason my own periods began getting shorter. “As a woman gets older, her menstrual cycles may become shorter,” Hack explains.  “This often becomes apparent in our 40s, especially in the years leading up to menopause.”

“It can be normal for period flow to vary from month to month and also change over time,” adds board-certified OB-GYN Sara Twogood, MD. I have enough other perimenopause symptoms that I’m currently managing—here’s looking at you, waking up for the day at 5 a.m. for no reason—that I’m confident it’s the culprit in my case.

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Premature Ovarian Failure

Known by the acronym POI, premature ovarian insufficiency means that your ovaries stop their work of producing eggs early, well before the standard age of menopause. It happens to about 1% of women and leads to irregular and/or light periods; it can also lead to them stopping completely. Because your ovaries stop making estrogen and progesterone when this happens, POI may lead to early menopause.

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Weight Change

Both losing weight and gaining weight can cause your periods to be suddenly shorter. Hack explains, “Rapid weight loss or gain can affect hormone levels and lead to shorter menstrual periods.” In response to weight changes, you body may produce more or less estrogen, offsetting your normal cycle with a different one.

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“Certain medications, such as birth control pills, can affect hormone levels and lead to shorter menstrual periods,” Hack tells us. While birth control is an obvious culprit, other medications, such as steroids and chemotherapy, can also lead to a shorter period. Hack says that “the period may return to its typical length once the medication is stopped.”

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Pregnancy and Postpartum

Your period may stop completely when you get pregnant, and it can also be different than you’re used to once it returns. “During pregnancy, menstrual periods will stop and can be shorter upon return of the period,” Hack tells us. “In addition, some women may experience implantation bleeding, which occurs when a fertilized egg implants in the uterine lining. This bleeding happens around the time of the expected period, however [it] typically only lasts one to two days.”

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Polycystic ovarian syndrome, known by the acronym PCOS, is an illness related to hormones. It causes your body to develop cysts in your ovaries that contain immature eggs, and it can mess with your cycle in many ways. Hack says that “polycystic ovary syndrome (PCOS) can also affect hormone levels and lead to shorter menstrual periods. These periods may also be infrequent.”

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Uterine Scarring

Often (but not always) caused by medical procedures, uterine scarring is trauma caused to the lining of the uterus. Possible causes include inflammation, endometriosis, or sexually transmitted diseases such as chlamydia, and the condition can contribute to shortened periods. Because the blood supply to the uterus isn’t ideal when this happens, uterine scarring may lead to infertility.

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Thyroid Disorder

Your thyroid, a tiny organ that lives in your neck, is considered the “master gland” of your endocrine system. Because of that, when it isn’t functioning properly, it can throw your hormones out of whack. A briefer period can be the result of hypothyroidism (when your thyroid is too slow), hyperthyroidism (when it’s too fast), or Hashimoto’s (an autoimmune condition in which your body attacks your thyroid).

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While pregnancy tends to stop periods completely, breastfeeding doesn’t necessarily. However, even if your cycle starts back up when you’re breastfeeding, it’s very normal to experience a shortened cycle. Often periods return after three to six months of breastfeeding, though it can also take until several months after you stop breastfeeding for that to happen.

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If you tend to work out more at some times than others, you may have noticed that your cycle shortens during more intense workout periods. “Regular, intense exercise can also affect hormones and lead to shorter menstrual periods,” Hack says. “If someone is undergoing strenuous training, their period may disappear altogether.”

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Hormonal Changes, Including Contraception

If you’ve ever been on the birth control pill, you know that skipping your off week is an option to prevent getting your period. In addition to this, the pill, IUDs, and other forms of hormonal birth control can lead to lighter periods without any effort on your part. “Hormonal contraception (progestin IUD, birth control pills) can make a period lighter, which is a great benefit,” Twogood says. Hack adds, “The menstrual cycle is controlled by hormones, and any changes in these hormones can affect the length of the menstrual period.”

The Final Takeaway

As you can see, there are many reasons why your period might have gotten shorter. Everything from short-term stress, which doesn’t usually require medical intervention, to PCOS or a thyroid disorder, which typically do, can cause you to bleed for less time. Twogood tells us that “irregular periods should be evaluated by your healthcare provider,” but notes that “it is normal for menstrual cycle length to fluctuate a bit.” If you’re worried that your period is shorter due to a medical condition, it’s wise to make an appointment with a provider.


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