Why Did I Miss My Period?

“Why did I miss my period?” Many of us have been there…you check your period tracker and notice you’re late and left wondering “where’s my period?”, only for it not to come at all. At this point, many people start to think “am I pregnant?” but there are actually multiple other reasons for a missed period!

Here’s a few possible reasons for missing a period:

1. Missed Period Due to Stress

High levels of stress are sometimes the culprit of a missed period. When our bodies are under stress, a hormone called cortisol is released. When cortisol is in the body it disrupts our other hormonal systems including our reproductive hormones. Our hormonal systems are very reliant upon one another to function in harmony and when cortisol spikes, it sends the rest of the systems into fight or flight mode.

Other systems in the body will shut down in response to this fight or flight signal to self-protect from the imminent threat perceived. This includes our reproductive functions which is why a missed period could be stress-related if you’ve had a difficult month¹.

2. Missed Period Due to Poor Sleep or New Sleep Schedule

If you’ve recently started working nights, swing shifts, or are up all hours of the evening finding rest difficult, that could be the reason for a skipped period. Our circadian rhythm (sleep schedule) is a key part of regulating hormones as our body does a lot of hormonal management while we’re asleep.

When sleep is disrupted and frequently changes, this can affect the rate of reproductive hormone production, resulting in late and missed periods². Poor sleep can also contribute to higher amounts of stress on the body, which we also know can be responsible for missed periods!

3. Missed Period Due to Weight Change or Fluctuations

Whether it’s gaining or losing weight, these changes to your body could result in a missed period. When the body gains or loses adipose tissue rapidly, it affects how the body builds and breaks down estrogen, which is a key hormone in periods³.

When it comes to rapid weight loss, the body once again enters fight or flight mode and may begin to shut down its systems, starting with menstruation. People with eating disorders or over-exercising may find they lose their periods because the body does not have enough nutrients to complete the menstrual cycle and must shut it down to keep the other vital systems functioning. This is an important thing to mention to your doctor if you experience lost periods in addition to disordered eating/exercising.

4. Missed Period Due to Pre-Existing Conditions (Or Undiagnosed Conditions)

Pre-existing conditions or unknown conditions could be responsible for irregular/missed periods. Reproductive conditions such as PCOS often cause missed periods due to insulin resistance and reproductive hormonal fluctuations. Conditions like endometriosis or even new cysts/polyps could possibly cause missed periods as well.

Conditions unrelated to the uterus can cause a missed period too. Thyroid disorders (both hypo or hyperthyroidism) can interfere with our reproductive hormones causing ovulation to be delayed or skipped resulting in an absent period.

5. Missed Period Due to Medications

Medications such as birth control, antidepressants, thyroid medication, hormone replacement therapy, and epilepsy medications can all affect the menstrual cycle. If you're starting new medications it may take your body’s hormonal system a month or so to adjust and regulate your menstrual cycle again. If you’ve been on a pre-existing prescription and notice missed periods, be sure to mention it to your doctor to rule out any other causes.

Sometimes even antibiotics can disrupt the menstrual cycle! Often a pharmacist will warn you upon administering medication if it could have menstrual cycle disturbances, but it doesn’t hurt to ask if they don’t mention anything.

6. Missed Period Due to Perimenopause

Perimenopause occurs a few years before menopause and greatly affects reproductive hormones that lead to irregular cycles. This generally happens when the body has started to run out of eggs in the ovaries and does not need to ovulate each month anymore, meaning infrequent periods. While the average age for perimenopause is when a person is in their 40s, some younger folks may experience perimenopause too, and it isn’t completely understood why. The irregularities in the body’s production of estrogen and progesterone at this time are a cause for irregular/missed periods⁴.

7. Missed Period Due to Pregnancy + Nursing

Pregnancy is a definitive way to see periods stop altogether. During pregnancy, ovulation stops, and with no eggs being released, there is no uterine lining to shed.

During the postpartum phase, nursing can also cause delayed and missed periods. There are strong hormones produced when lactation happens in the body, and this often suppresses the menstrual cycle (but not always). Many people will not resume a period until they are done nursing, but even then, it may be irregular for a few months until the hormones have all straightened themselves out.

When to See A Doctor

When pregnancy has been ruled out, see your doctor after more than three missed periods. The hormones involved in menstruation regulate other systems in the body as well such as mood, heart, and bone health. (Learn more about when you should see a doctor for other period health concerns here.) It’s important to know the cause of recurring missed periods to promote overall wellbeing and health. I also recommend tracking your menstrual cycle so you can report any other symptoms, including irregular periods, to your health care provider.

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