Common reasons for a missed period

I get phone calls quite often from patients because of a missed period. Sometimes it’s an excited phone call – “I had a positive pregnancy test and I’m so excited”. Sometimes it’s a not-excited phone call – “My period is late but I’m not sure if I’m pregnant or not and I really hope I’m not”. Sometimes it’s a worried call – “I missed my period and I’m worried something is wrong”. 

Photo: Noah Bartscher

So let’s go through some reasons for a missed periods and what to do about it!

1. Pregnancy! 

This is an obvious one. If you miss your period, you need to think about it! If you’re having unprotected sex, or using contraception but not perfectly, then a pregnancy test is a good first step. This is one of the first things your doctor evaluates you for as well. Is a home pregnancy test accurate or do you need to see a doctor to take one? Urine home pregnancy tests are the same urine tests we use at the office! So yes, if you are already a few days late then a home pregnancy test should be accurate.

2. Stress 

This is anecdotal for sure, but during the pandemic, more and more people were having irregular periods. It could have been that people were just paying closer attention to their bodies, or maybe it was the weight gain that was so common (see #4 below), or perhaps it was the change in day to day behavior (see #3 below). But we can’t discount that everyone was experiencing an extreme amount of stress. 

This is the way I explain it: your body senses something is amiss. Cortisol (the stress hormone) is elevated, causing physiologic changes to your body. Is this an optimal time to ovulate? Is this an optimal time to start a pregnancy? Nope! Your body doesn’t ovulate so a period doesn’t come. 

3. Changes in day to day behavior

Big life events or significant changes in routine can shift periods, for likely the same physiologic reasons as stress. An example is a big vacation. We don’t think of that as “stressful”, but changes in food, diet, daily activities, irregular sleep, and circadian rhythm all come in to play.

4. Significant and sudden changes of weight – both weight gain and weight loss

One theory behind this reason is that we carry hormones in our fat cells – when these hormones change rapidly, our hormones can change, and that screws up our cycles. 

5. Polycystic ovarian syndrome can cause irregular periods

Here’s a great post about PCOS!

6. Thyroid disorders

The thyroid is a remarkable gland and thyroid hormone contributes to regulating so many bodily functions, including our menstrual cycles. High or low thyroid levels can alter periods – causing frequent or infrequent and irregular periods (in addition to many other symptoms!). This can be tested through blood work as well. 

7. Elevated prolactin level

Prolactin is a hormone secreted from the pituitary gland in the brain. It’s elevated during breastfeeding which is why, in general, breastfeeding suppressed periods. There is also something called a pituitary adenoma – this is a small cluster of cells in the pituitary that grow and secrete an abnormal amount of prolactin. Beside missed periods, milk production from the breasts no where near a pregnancy may be a sign of a high prolactin. A level can be checked by a blood test. 

8. Use of emergency contraception, like Plan B

Emergency contraceptive pills work in a few ways, depending on when in a cycle they are taken. They can thicken cervical mucus, alter fallopian tube functioning, and / or delay ovulation. The delay in ovulation subsequently delays the next period. Also, a big surge and then drop of progesterone at some random time in the cycle can cause spotting or bleeding that’s not a period. 

9. Hormonal birth control – birth control pills, IUDs, Nexplanon, Depo Provera

All hormonal contraception can change periods. We often use them to intentionally change periods for the better – make them more predictable or lighter flow or less painful. But some of these hormonal contraceptives (particularly the IUD, Nexplanon, and Depo Provera) can cause irregular or unpredictable bleeding. 

10. Other medications

Spironolactone, a medication used for acne, is often a culprit behind irregular periods. And some anti-depressants have been reported to cause some initial changes in periods too. This may be linked to a change in weight experienced with SSRI / SNRI or from the mental health component (not just the medication itself). But take a peek at your medications and supplements as a potential cause too!

What if it’s none of these? When should I worry? 

A rule of thumb I tell my patients: if there is no pregnancy, one late or missed period is often nothing to worry about! Tracking periods with an app or calendar can help you see if this is an anomaly or if periods are erratic. If periods are unpredictable and irregular, or it’s been months since a last period, it’s a good idea to schedule an appointment to look into things a bit more! 


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