What is a one-sentence summary of the following article?
Abnormal vaginal bleeding is often one of the first symptoms of an ectopic pregnancy. This bleeding may be either heavier or lighter than what you normally experience during your menstrual period. It may also be accompanied by severe pelvic or abdominal pain. If you experience vaginal bleeding when you know you are pregnant, or if the vaginal bleeding is accompanied by severe pain or lightheadedness, seek medical attention right away. If you have pain in your lower abdomen or pelvic area, or cramping on one side of your pelvis, you may have an ectopic pregnancy. If this pain persists, worsens, or occurs with any other symptoms (such as vaginal bleeding), call your doctor or go to the emergency room right away. This pain may feel sharp or stabbing, and its intensity may vary from one moment to another. Ectopic pregnancy is sometimes accompanied by a sharp pain that radiates into the shoulder and neck. If you experience this symptom, especially if you know you are pregnant and/or the pain is accompanied by other symptoms (such as pelvic pain and vaginal bleeding), seek emergency medical care immediately. An ectopic pregnancy may rupture if left untreated, causing severe internal bleeding. Seek emergency medical care immediately if you experience the following symptoms of a ruptured ectopic pregnancy:  Sudden, severe abdominal or pelvic pain that lasts for more than a few minutes. Light-headedness or dizziness. Stabbing pain in the shoulder or neck. This may be caused by blood in the abdomen or under the diaphragm putting pressure on nerves that run to your shoulder. A sensation of pain or pressure in your rectum (this may feel like an urgent need to have a bowel movement). This may be a sign of internal bleeding, which needs immediate medical treatment. Low blood pressure. Nausea and vomiting. Pain on 1 side of your body. Sharp abdominal cramps. Weakness. Fainting.

Summary:
Note vaginal bleeding. Take abdominal or pelvic pain seriously. Check for shoulder pain. Go to the emergency room for severe symptoms.