Why does miscarriage cause bleeding in early pregnancy?

When a pregnancy stops developing, the connection between pregnancy tissue and the uterine lining can loosen. Blood vessels in that lining may open, causing spotting or bleeding. The uterus can contract and pass tissue, which may bring cramps, clots or stronger bleeding. The pattern can vary, and bleeding may begin before tissue passes or continue afterwards. Bleeding in early pregnancy has other possible causes, including changes at the cervix, infection and ectopic pregnancy, so the symptom needs assessment rather than a conclusion based on bleeding alone.

Contact a maternity service, doctor or emergency service for advice about any bleeding in early pregnancy. Note when it started, how quickly pads become wet, whether you pass clots or tissue, and whether pain is on one side. Do not put anything into the vagina until you have received medical advice if bleeding is active. Assessment may include questions, an examination, blood tests or an ultrasound, depending on the pregnancy stage and symptoms.

Seek emergency care for heavy or rapidly increasing bleeding, severe or one-sided abdominal pain, shoulder-tip pain, fainting, marked dizziness, fever or feeling very unwell. These signs can indicate significant blood loss, infection or an ectopic pregnancy. Even light bleeding should be discussed promptly because only an assessment can show what is happening with the pregnancy.

How much bleeding should prompt emergency care? Do my pain or bleeding need an ultrasound or blood tests? What symptoms should I monitor at home? If this is a miscarriage, what follow-up and support will I receive?