Can Stress Cause Bleeding Between Periods?

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In some rare cases, excessive stress causes bleeding between periods. It is more common that another condition is responsible, such as pregnancy, polycystic ovary syndrome, infection, pelvic inflammatory disease or side effects of medication, according to WebMD. Bleeding between periods sometimes also indicates rarer but more serious conditions, such as uterine fibroids, polyps, cancer of the reproductive organs, hypothyroidism or diabetes.