You’re expecting your period, but it fails to show up. What 's going on? Even if your periods tend to be regular – arriving at intervals of between 28 and 35 days – an occasional delay, or even a skipped period, is normal. It can happen if you’re experiencing a lot of stress, if you exercise a lot, or if your weight has changed dramatically. But if your period stops for several months and you’re not pregnant, you should visit your doctor to investigate the cause and find a solution.

The onset of menstruation indicates the beginning of the fertile phase of a woman's life. Pregnancy is the most common reason that periods stop when a woman is sexually active. If that describes you, see a doctor right away.  He or she will do a blood test to confirm if you’re pregnant, and is you are, they’ll start the medical care necessary for you and for the baby growing inside you.

However, there are other reasons that periods can stop. Medically, the absence of periods is called amenorrhea. There is primary amenorrhea and secondary amenorrhea. The first occurs when periods don’t start at around the average age. It's not frequent, but it does affect about one in every 300 teens. When your periods stop after you start menstruating, it’s known as secondary amenorrhea. It is estimated that it affects one in 25 women at some point in their lives. It is more common in teenagers and younger women and occurs more frequently in certain groups, such as professional athletes, dancers and gymnasts.

Have you had changes in your daily life? Are you under a lot of stress? Has your weight changed? Have you started taking a new medication? These, among other reasons, could be the reason your periods have stopped. Here are the most common causes for period cessation:

• Lifestyle factors: Excess stress can temporarily affect an area of your brain, the hypothalamus, which regulates the hormones that control your menstrual cycle. Once the stress is controlled or disappears, your periods will return to their normal frequency. Your periods can also be affected if you’ve had a sudden and extreme weight loss, as happens in people with eating disorders like bulimia and anorexia. This can alter your normal hormone levels, disrupting menstruation. Or, if you participate in sports that require rigorous training like gymnastics, track or ballet, don’t be surprised if your periods stop.
• Taking certain medications: Your periods could stop if you need medication for high blood pressure, if you take an antipsychotic (for autism, bipolar disorder or attention deficit hyperactivity disorder, for example), if you take antidepressants or if you’re undergoing chemotherapy to treat cancer.
• Hormonal changes: Some medical conditions can cause hormonal imbalances affecting menstruation. These include tumors in the pituitary gland (located in the brain), if your thyroid gland doesn’t function properly, and polycystic ovary syndrome.

These are just a few of the possible causes. I recommend that you visit your primary care physician or gynecologist if your period goes missing for two or three months and you’re not pregnant, or if you have not menstruated by your 17th birthday. The doctor will determine the cause and begin treatment.

Don’t be ashamed to talk to your parents and/or a health professional about this. It’s always better to take action early in order to avoid major problems in the long term. It’s possible that in your case everything will get back to normal after some minor adjustments to your environment or your lifestyle. It’s important that you learn to know and respect your body and how it works. This includes your period and everything that could affect it.

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