Main Causes of Irregular Periods

Irregular Periods

You’ve probably heard menstruation referred to as “that time of the month.” For many women, having a period is a regular monthly occurrence. So what does it mean if your periods are few and far between, or irregular?

What Is an Irregular Period?

Generally speaking, a 21- to 35-day cycle is considered normal. You don’t need to have exactly 12 periods in 12 months for it to count as a “regular” cycle. The variation in your cycle also matters. If you’re trying to get pregnant, a medical provider may expect to see no more than about 4-5 days of variation. While a 23-day cycle might be standard issue for one person, it could be cause for concern if another person swings between a 23-day and a 34-day cycle, for example.

Here are the top reasons why you might experience irregular periods.

Thyroid Issues

Hormones aren’t limited to one area of the body. They affect each other. Imbalanced hormones in one organ can have something almost like a domino effect, triggering over- or underproduction of other hormones.

Your thyroid is a butterfly-shaped organ in your throat. It helps regulate your metabolism and produces hormones that contribute to the function of several major systems in your body. Hypothyroidism can lead to lighter, more frequent periods, while hyperthyroidism can make them less frequent and heavy. Your doctor can prescribe medication to regulate your thyroid, which can help resolve menstrual issues.

Polycystic Ovary Syndrome

PCOS is the most common cause of infertility in women in the United States. Many women have this condition without realizing it. PCOS also stems from hormone imbalance. Besides the characteristic, tiny cysts on the ovaries, PCOS is often associated with excess hair growth, weight gain, and skipped periods. Because PCOS can prevent you from ovulating normally, you’ll want to consult a doctor when you’re ready to try for a baby to discuss any measures you might need to take to regulate ovulation.

Uterine Obstructions

Growths in your uterus, such as fibroids or polyps, can cause heavy, painful periods. People who have had a C-section or D&C may develop persistent scar tissue in the uterus, a condition known as Asherman’s syndrome. Asherman’s can cause scanty or missed periods, and the scar tissue can make it difficult for a fertilized embryo to implant, even if ovulation happens normally.

Pelvic Inflammatory Disease

PID is an infection of the reproductive organs. It’s caused by bacteria making its way up the reproductive tract. Untreated STDs are a common cause, although not the only potential cause. Pregnancy, miscarriage, abortion, or some gynecological procedures can also introduce bacteria into the body. PID can cause infertility by causing too much scar tissue to build up. Irregular periods along with other symptoms like abdominal pain, vaginal discharge, nausea, and fever can indicate this disease.


Endometriosis is a condition where the uterine lining (that develops each month to nurture and shelter a potential fertilized egg) doesn’t grow the way it’s supposed to. The body may make too much endometrial tissue that builds up over time. Endometrium may also grow in other areas where it shouldn’t be. This often causes heavy, very painful periods, and it can also cause spotting between periods. If your menstrual cycle is painful, and if it’s been getting worse over time, tell your medical provider. Sometimes women think their period is “normal” because they developed endometriosis early and don’t have another experience to compare it to.


Serious, chronic stress can affect your menstrual cycle. This can be emotional stress, like a hostile work environment or family member with a severe illness. Physical stress, like the rigors of military life or professional athletic training, can also interfere with the typical menstrual cycle. Taking measures to lower stress (and the stress hormone, cortisol–remember that hormones affect one another) and get adequate sleep can help. Avoiding extreme intensity or frequency of exercise can also help get periods back on track.

Jessica Sillers
Jessica Sillers is a parenting and finance writer whose work has been featured in Pregnancy & Newborn, Headspace, and more. As a new mom herself, she’s passionate about helping other parents find the community and support they need. When she’s not writing, she loves spending time with her family, reading, and hiking.

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