Irregular Period and Pregnancy: What To Know

Some people seem to have it all, including an easy, painless period that happens once every 28 days.

For the rest of us, irregular periods are pretty standard. Most people of menstruating age will experience irregular periods at least once in their life. 

While it can be frustrating, having an irregular period (a period that isn’t consistent from month to month) can make it more difficult to know your fertility window if you are trying to become pregnant

We’ll cover what a “normal” period is and what makes a period irregular. We’ll also cover what causes irregular periods and how you can determine when you are ovulating with an irregular period. 

What’s a Normal Period?

It can be hard to define what is normal and what is not when it comes to having a period. Every person and body is different, but generally, a period cycle lasts 28 days.

During the 28-day cycle, you’ll experience four distinct phases. 

Menstrual Phase

This phase begins on the first day of your period and ends on the last day. Roughly, it should last between five and eight days.

During this first phase of the menstrual cycle, your body releases an unfertilized egg and sheds the lining of your uterus.

Follicular Phase

Overlapping with the menstrual phase is the follicular phase, which also starts on the first day of your period and lasts about 16 days.

During this phase, hormones in your body stimulate your ovaries to produce follicles. Each ovary produces between five and 20 follicles which will house an immature egg that could be released. 

Ovulation Phase

The shortest menstrual cycle phase is the ovulation phase, which lasts only 24 hours.

During the ovulation phase, luteinizing hormones cause your body to release one mature egg from one ovary to travel down the fallopian tube to your uterus. Once in the uterus, the egg can be fertilized.

Luteal Phase

During the luteal phase, your body prepares for a potential pregnancy. The follicle that releases the egg will begin to release progesterone and estrogen to keep the lining of the uterus thick and sticky.

If the egg is fertilized, this will help the egg implant into the uterus successfully. 

The luteal phase lasts between 11 and 17 days, ending on the first day of your next period.

If the egg is fertilized, you may not have another menstrual phase unless you have a complication.

Each person’s cycle is different, and as you age, your cycles will begin to change.

If you experienced regularity in your twenties, you might notice that your cycles become “irregular” after you’ve had a baby or as you enter your forties. 

What Is an Irregular Period?

An irregular period is a period that does not track a regular cycle from month to month.

For instance, if your monthly cycle only lasts 26 days as opposed to 28, that is not an irregular period because it is regular for your body.

An irregular period might last 22 days one month, 30 the next, and 28 the third month.

Sometimes, irregular periods mean skipping a period altogether, a common occurrence in perimenopausal people. 

Irregular periods come late, early, or not at all. They also may start and stop and restart again a few days later.

These changes are most commonly associated with puberty and menopause, but there can be other causes that could interfere with your ability to become pregnant. 

Another common symptom of an irregular period is excess cramping, abnormal uterine bleeding, and increased PMS-like symptoms. 

Causes of Irregular Periods

Having an irregular period isn’t necessarily a cause for concern.

Irregular periods can be common during some stages of life or due to certain lifestyle situations. 


People who have just started their periods may experience irregularity for the first few years of menstruation.

Along with irregularity, they may also experience incredibly light periods with heavy cramping. 


Most menstruating people will reach menopause between the ages of 45 and 55, which means that menstruation stops.

Before menopause, however, you may experience periods that become irregular. Periods may start and stop every few months, vary from light to heavy, and last longer or shorter than usual. 

Birth Control

Certain types of birth control can cause irregular periods initially, but the period usually becomes more predictable the longer the person is on the specific type of birth control. Intrauterine devices (IUDs) can cause period irregularity, as can oral contraceptive pills.

Changes in Weight

Extreme weight loss can cause amenorrhea, which is the loss of your period. Extreme weight gain can also cause a change in your monthly cycle.

Excess weight gain or loss can also be a symptom of a more serious medical condition that you can discuss with your healthcare provider. 

Similarly, excessive exercise and eating disorders can lead to irregular periods. Being underweight can cause significant menstrual irregularities, so talk to your doctor. 

Polycystic Ovary Syndrome (PCOS)

This condition causes your ovaries to release eggs with irregularity (irregular ovulation).

Instead of releasing an egg for fertilization each month, your body will produce follicles (not cysts as the name suggests) but may or may not release an egg each month during ovulation. 

This medical condition causes period irregularity and causes androgen levels to rise.

About 21 percent of menstruating people have polycystic ovarian syndrome, usually due to genetics, excess weight, or lifestyle choices. 

Thyroid Disease

The thyroid is an organ located at the base of your neck that regulates certain hormones.

If you have thyroid disease or issues related to the thyroid, the hormones that regulate your periods may be affected. 

Hypothyroidism and hyperthyroidism can cause irregular menstrual bleeding and other symptoms


High stress levels negatively impact your health, including your menstrual cycle.

Stress causes the hormone cortisol to be released, which can affect your reproductive system and be a common cause of an irregular or missed period

If your stress levels remain high for a longer period (becoming chronic stress), it can cause you to miss a period for several months. 

Uterine Polyps or Fibroids

These noncancerous tumors can form in the uterus and normally cause painful, heavy periods. However, in some cases, they can also cause menstrual irregularity. 

You will need an ultrasound to determine if you have developed these benign growths.

Your doctor or OB-GYN can help determine how best to proceed and whether or not you need to have them removed. 


Endometrial tissue lines the uterus, and each month if you do not become pregnant, the tissue s discarded in the menstrual phase of your monthly cycle.

If you develop endometriosis, endometrial tissue will begin to grow outside of the uterus, attaching to fallopian tubes, ovaries, and sometimes even your intestines. 

This condition is painful, causes heavy or irregular periods, and can make it difficult for you to become pregnant. You may need a surgical procedure to remove endometrial tissue. 

Pelvic-Inflammatory Disease (PID)

This disease is usually transmitted via sexual intercourse.

PID can cause you to experience heavy, uncomfortable periods and can come with a host of side effects like:

  • Nausea
  • Vomiting
  • Fever
  • Diarrhea
  • Vaginal discharge with an unpleasant odor

Talk to your doctor immediately if you are pregnant and develop these symptoms. PID can endanger your pregnancy and needs medical attention

Premature Ovarian Insufficiency 

In people under 40, premature ovarian insufficiency can cause menopause-like symptoms, including losing your period.

If you have family members who have a history of this disease, you are more likely to develop it yourself. 

Other causes of premature ovarian insufficiency can be medical treatments and other underlying diseases. 

Irregular Periods and Your Fertile Window

If you are trying to become pregnant, an irregular menstrual cycle can make it difficult for you to calculate your ovulation date or determine when you’ll most likely get pregnant

Understanding the Fertile Window

Your fertile window is the time when it is most likely you will become pregnant. This window is usually calculated as a few days before you ovulate, the day you ovulate, and two days after you ovulate.

It is more likely that the egg your body releases will be available for fertilization and implantation during this time. 

Calculating the Fertile Window

To calculate your fertile window, you will need to be able to track your monthly cycle for at least three months.

If you have an irregular period, getting a three-month average can be virtually impossible. 

If you have trouble determining your fertile window due to an irregular period, it may be that you do not ovulate on a regular cycle. It can also mean that you don’t ovulate every single month. 

Irregular Periods and Ovulation

You do not have to have the menstrual phase of your menstrual cycle (your period) to ovulate.

Conversely, you can also have a period without ovulation. Some of the conditions above can cause either of these scenarios to happen. 

If you are attempting to get pregnant and having difficulty, your doctor will test for these conditions to determine when and how frequently you ovulate. 

Talk to your doctor about your options if it takes you longer than a year to get pregnant. 

Pregnancy and Irregular Periods: What You Can Do

If you suffer from irregular periods and want to become pregnant, you can take steps to help determine your fertile window and increase your chances of becoming pregnant

Paying closer attention to your body can help you hone in on your fertile window and learn when your body is ovulating.

Here are three signs you are getting ready for ovulation. 

1. Cervical Mucus

The discharge after your period can be annoying, especially if you’ve forgotten to use a pantyliner. This discharge, usually thick, white, and mucus-like, appears just a few days before ovulating. 

2. Increased Temperature

Immediately after you ovulate, your body temperature will rise by half or a whole degree and may stay this way for up to 24 hours.

Taking your temperature every morning when you get out of bed and charting it throughout the month can help determine if you have ovulated. 

Seeing your basal body temperature rise can indicate that you have ovulated and are currently in your fertile window.

3. Ovulation Predictors

Ovulation prediction kits can help you predict when ovulation is near.

They test for luteinizing hormone, the hormone your body releases to trigger the release of an egg from the follicle sacs during the ovulation period. 

You can take these tests as soon as your period is over, and they are effortless to use (much like a pregnancy test). Unfortunately, to determine when you are fertile, you’ll need to take a test daily, which can become expensive if you are trying for several months to become pregnant. 

Supporting Healthy Pregnancy Goals

Attempting to become pregnant can be difficult if you have an irregular period, but it is possible. Begin by taking care of your body by exercising regularly, eating healthfully, and starting a prenatal vitamin. 

If you continue having difficulty becoming pregnant, talk to your doctor. Numerous treatment options are available to help you overcome fertility issues and make you more likely to become pregnant

References, Studies and Sources:

Life-Style and Reproductive Factors Associated with Follicular Phase Length | PMC

Irregular periods | NHS 

Polycystic ovary syndrome | MedlinePlus Genetics 

Can Stress Cause You To Skip A Period? | Cleveland Clinic

Abnormal Menstruation (Periods): Types, Causes & Treatment | Cleveland Clinic