Irregular Periods & The Causes

July 8, 2022

Many women have menstrual periods that last anywhere from 4 to 7 days. A woman’s period usually occurs every 28 days, but normal menstrual cycles generally range from 21 days to 35 days. Maybe you have had normal cycles but suddenly experience irregular periods and are concerned. Ready to learn more about irregular periods and why they happen?

Your periods can be irregular if your menstrual cycle is shorter or longer than average.  This means the first day of your last period started less than 24 days of your current cycle or there is more than a 38-day time span. An example would be if your cycle jumped from a normal 25-day cycle to a 46-day cycle and then back to a 25-day cycle in the following month.

Teenagers & Perimenopausal Women

Irregular periods can be considered normal for teenage girls and perimenopausal women. For teens, it is common for their periods to be irregular in the beginning.  They generally become more predictable with time.  When women begin to transition to menopause, also known as perimenopause, their menstrual cycles may become more irregular over time.

What Causes Irregular Periods?

  • Eating disorders can cause irregular or missed periods.  Including anorexia, bulimia nervosa, and a binge eating disorder.
  • Thyroid problems, such as hyperthyroidism can interfere with your period. Hyperthyroidism, or overactive thyroid, causes your thyroid to make more thyroid hormone than your body needs. Hyperthyroidism can also cause fewer and lighter menstrual periods than normal.
  • High amounts of prolactin in the blood. This condition is called hyperprolactinemia. Prolactin is the hormone that causes breasts to grow during puberty and makes breast milk after childbirth. It also helps to control the menstrual cycle.
  • Certain medicines such as those for epilepsy or anxiety can change your menstrual cycle.  Make sure to look at the side effects of any medication you are taking.
  • Polycystic ovary syndrome (PCOS), is a condition that usually causes multiple ovarian cysts, hormonal imbalance, and irregular periods. About 1 in 10 women who experience irregular menstrual cycles have PCOS.
  • Primary ovarian insufficiency (POI). POI happens when your ovaries stop working normally before age 40. Primary ovarian insufficiency is sometimes confused with premature menopause, but these conditions aren’t the same. Women with primary ovarian insufficiency can have irregular or occasional periods for years and might even get pregnant. 
  • Pelvic inflammatory disease (PID). Pelvic inflammatory disease (PID) is an infection of the female reproductive organs. It most often occurs when sexually transmitted bacteria spread from your vagina to your uterus, fallopian tubes, or ovaries.
  • Stress. Studies show high levels of chronic (long-term) stress can lead to irregular periods.
  • Uncontrolled diabetes. Type 1 and type 2 diabetes can cause irregular periods, but getting your diabetes under control can help your periods to become more regular.
  • Obesity. The extra fat in the body makes the hormone estrogen. The extra estrogen changes the normal menstrual cycle and can cause missed, irregular, or heavy periods.

When To Talk To You Doctor

  • When you suddenly experience irregular periods after years of having normal cycles.
  • When your period happens more often than every 24 days or less often than every 38 days.


Treatment will depend on each individual case.  Your doctor may recommend hormonal birth control, such as a hormonal IUD, the pill, shot, or vaginal ring, to help control your menstrual cycle. Hormonal birth control is sometimes prescribed by doctors for women’s health concerns other than preventing pregnancy.

At OB-GYN Women’s Centre, we help you through every stage of life.  Remember you are not alone, we can help you with any concerns you may have.  It is easy to schedule your appointment online or call us at (941) 907-3008.