9 causes of a late period and when to take a pregnancy test

• A late period can be caused by being under or overweight, changes in birth control, and pregnancy.
• If it has been more than 30 days since your last period, you should take a pregnancy test.
• If you're pregnancy test is negative and your period hasn't arrived, see a doctor.

A missing or late period can be a stressful experience. Menstrual cycles vary in length from person to person, so a late period is relative. The average menstrual cycle length is 28 days, but it can range from 21 to 45 days depending on your age.

A late period, says Jennifer Lincoln, MD, an OB-GYN at Providence Health & Services Oregon, is any period that comes after you would normally expect it depending on your cycle length. It can be caused by a number of situations, from stress to pregnancy.

Here are some reasons your period may be late and when you may need to see a doctor.

1. Exercising more than usual

Lincoln says a new exercise regime can impact your period, and these effects are heightened with extreme exercise. High amounts of physical activity can impact certain hormones involved with the menstrual cycle.

2. Pregnancy

This is typically the first thing on peoples' minds when they miss a period, Lincoln says. You can take a pregnancy test on the day your period was scheduled to come if you think you may be pregnant.

3. Stress

This is a common reason for irregular periods. "Think about it from an evolutionary standpoint: if you are stressed, it isn't a great time to get pregnant, so your body is putting its energy elsewhere," says Lincoln.

4. Changes in birth control

"Having a late or no period is very common with many forms of birth control," Lincoln says. Many people safely use birth control to have light periods, or skip them entirely. But if this is a new issue, Lincoln says, ask your doctor about it.

5. PCOS

Polycystic ovary syndrome, or PCOS, is caused by a hormonal imbalance that impacts around 10%of people of childbearing age. "One of the hallmarks of PCOS is anovulation, or not releasing an egg regularly. This can lead to irregular periods and what we call anovulatory bleeding," Lincoln says. It can also lead to missed periods or prolonged periods

6. Low body weight

"If your body is underweight or undernourished, it isn't going to be able to support a pregnancy, so your body goes into survival mode and scraps ovulation," Lincoln says.

7. Obesity

The additional fat tissue in overweight people can produce extra estrogen. This can mess with your body's normal menstrual cycle, says Lincoln.

8. Irregular thyroid hormone levels

The thyroid is a gland that produces hormones and regulates metabolism. If you have a thyroid disease like Hashimoto's disease, the imbalance of hormones may impact your menstrual cycle.

9. Menopause

"The average age of menopause is 52 in the United States, and by definition it means not having a period for 12 months. However, periods can be irregular in the time leading up to this, called perimenopause," says Lincoln. If you notice you have irregular periods along with other symptoms of menopause such as hot flashes much earlier than your late 40s, you should talk to your doctor.

How late is too late for your period?

Because menstrual cycles can vary from person to person, Lincoln recommends you track your cycle to figure out what is normal for you.

Related Article Module: When to take a pregnancy test for the most accurate result

If you typically have regular cycles and your period is late, you may want to take a pregnancy test. "The best time to test is to wait until you've missed your expected period, but some can detect pregnancy a few days earlier than this. If you got a negative early test and your period still doesn't show up, you can test again," Lincoln says.

If you're not pregnant, and you still aren't getting your period, you should see your doctor. "The missing period is a symptom, not a diagnosis, so it's important to figure out why it isn't there," Lincoln says.

Insider's takeaway

There are a number of reasons your period may be late or missing, ranging from thyroid disease, stress, exercise, new birth control or pregnancy. A late period is a symptom of many conditions, so you should see a doctor when your period is atypically late or missing.

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