OB/GYNs Explain 8 Little-Known Reasons Your Period Could Be Late

by Gina M. Florio and JR Thorpe
Originally Published: 
A woman holds a menstrual cup and a bunch of tampons. These reasons your period could be late are li...
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If you're a menstruating person, then you already know that far too much of life is spent waiting for late a period to show up. It can be one of the most infuriating things, especially if you've already been battling annoying PMS symptoms for a while, like bloating, fatigue, and bizarre food cravings. When your period finally does arrive, though, most of us don't even bother to poke around and find out what the reason for our period being late was.

But it might be worth our time to dig a little deeper and understand what's responsible for a late period. In some cases, it might point to a health issue that has been previously overlooked. Other times, it could be something harmless, but knowing about it can help us prepare better so we don't have to play the anxious waiting game again in the future. "Every cycle is unique, and some are more sensitive to changes in things such as sleeping patterns and eating habits," Anna Druet, a research scientist at menstrual app Clue, tells Bustle. That's why it always helps to keep track of when your period normally comes and ends, so when something seems off, you can take note of it and see if it's worth looking at with your doctor.

But what's "late," exactly? A run-of-the-mill menstrual cycle generally falls between 21 and 35 days, but it's different for everyone. However, you should have consistency in whatever number of days your cycle is — that's what makes a "normal" period for you. If your period is five or more days late with respect to your "normal," something is probably going on, even if it's nothing too serious. Finally, if you're keeping track of your cycle and see that three or more months in a row have been irregular, call up your provider and see if you can schedule an appointment to uncover what's going on.

Here are eight reasons your period might be late that you probably haven't considered.

1. You Recently Took An International Flight

When we travel across time zones, "the loss or gain of hours... affects your circadian rhythm, which in turn influences the hormones that regulate your menstrual cycle," Druet says.

Because our circadian rhythm is intimately connected with our menstrual cycles, it could take a period or two before your hormones are back in balance with the time zone you've settled into. So don't be surprised if your period decides to be extra stubborn when you and your bestie take that trip to Europe you've been planning for a while. "Also, be aware that your fertile window may be different," Druet advises.

2. You're Extremely Stressed Out

"A variety of factors can impact periods, including significant stress," Dr. Felice Gersh M.D., an OB/GYN, tells Bustle. Stress takes a toll on the body, particularly when in large quantities, because it can throw off the connection between the pituitary gland and our ovaries. An off-kilter ovulation can make your period come a bit later than usual. (Keep in mind, though, that if you're on a hormonal form of birth control, this won't be the case, since the contraception you're taking will guide your menstruation, not your ovulation.)

If you're going through a particularly stressful time, like a breakup or starting a new job, your period may decide to hold off on you for a little while. If this keeps happening for a while, though, you might be chronically stressed out, which means you should consider making some lifestyle changes or at the very least, go see a doctor. Letting this kind of heavy stress take over may result in amenorrhea, which is the loss of your period entirely.

3. You've Gained Or Lost A Significant Amount Of Weight

Extreme changes in your weight can affect when your period arrives, Dr. Gersh says. Though body mass index (BMI) is beginning to be considered a not-great measure of health, a sudden change in weight can be an indicator of stress on your body. If your BMI falls below 18 or 19, for example, you may even start missing periods altogether. Similarly, sudden weight gain could result in irregular periods as well. "Fad or crash diets, fasting, and thyroid dysfunction can all impact your period," Dr. Gersh says.

4. You're Sick, Or You Were Not Long Ago

Things like the flu or a stomach virus may not hurt you in the long run, but they could have an impact on your next menstrual cycle. Your body simply doesn't function the same way when you're feeling sick, Dr. Gersh says. If you're experiencing noticeable changes in your digestion or respiratory health, it's possible that your reproductive system has taken a hit, too. You should be back to normal when you start feeling 100% again. (Like stress, this only applies to you if you're not taking hormonal birth control.)

5. You've Recently Experienced Significant Changes In Your Life

Druet tells Bustle that changes in sleep patterns, work hours, or even moving can affect your menstrual cycle, just like international travel can. This "will have a greater impact on your cycle as it is harder for your body to adjust to losing time," Druet says.

No matter how minor you think the changes in your life may be, remember that your menstrual cycle doesn't exist in a vacuum. It's affected by the rest of your body and the myriad of your lifestyle choices, since they all have an effect on the balance your hormones.

6. You've Been Exercising Excessively

If you've recently beefed up your exercise regimen, your body may react to the sudden changes, potentially resulting in late periods or no periods at all, Dr. Gersh tells Bustle. Before you cancel your gym membership, know that the definition of excessive exercise doesn't simply mean you've run a few extra miles on the treadmill and exhausted yourself. This happens because the stress you put yourself through with such rigorous exercise causes your body to do anything it can to prevent pregnancy. Ovulation gets thrown off, you have less estrogen in your system, your uterine lining doesn't thicken, and subsequently, your period may be a bit tardy.

7. You Just Changed Or Stopped Using Birth Control

If an imbalance in your hormones causes a late period, you can bet a change in birth control methods can cause a delayed period. When you start a new regimen of contraception, your hormones need time to adjust and introduce your body to a cycle. It's just as probable that you see odd delays in your period when you choose to quit your birth control as well; your body is recalibrating to its own rhythm, so give it some time to fall back into the swing of things. Talk to your doctor if your period doesn't stabilize in two or three cycles.

8. You Have An Illness Or Disorder That Hasn't Been Diagnosed Yet

Having late or irregular periods can be a sign that something more serious may be going on. Dr. Gersh names polycystic ovary syndrome, thyroid dysfunction, and pituitary tumors as potential medical conditions that can cause menstrual dysfunction.

An overactive thyroid can cause delays in menstruation, a strangely light flow, or skipped periods altogether. Non-period related symptoms that point to a thyroid issue include diarrhea, muscle weakness, sudden weight loss, and a racing heart. Polycystic ovary syndrome (PCOS) is a hormone imbalance that sends abnormal levels of estrogen, testosterone, and progesterone through the body and causes lack of ovulation. Other symptoms are infertility and the growth of hair in odd places, so if you've encountered any of these, speak to your doctor. Pituitary tumors develop on the pituitary gland on the base of the brain; they're usually benign — but they can cause period irregularities, headaches, and sometimes milk production, too.

If any of the above sounds familiar, it's best to schedule a visit with your doctor. No matter what, know that your period is an important vital sign that can help your doctor figure out what's going on with you. Don't hesitate to speak with your provider — because, as annoying as periods can be sometimes, they're a pretty good indicator of what's going on with the rest of our health.


Anna Druet, research scientist, Clue

Dr. Felice Gersh M.D., OB/GYN

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