Threatened abortion: This is the most common cause of vaginal bleeding in early pregnancy, accounting for up to 50% of cases. It is characterized by bleeding with or without cramping, but the cervix remains closed.

Miscarriage: Also known as spontaneous abortion, this is a common cause of vaginal bleeding in early pregnancy. It can be further divided into inevitable, incomplete, or complete miscarriage, depending on the status of the cervix and the passage of products of conception.
Ectopic pregnancy: Although less common than threatened abortion or miscarriage, ectopic pregnancy is an important consideration, especially if there is associated abdominal pain or a history of risk factors such as tubal damage.
Subchorionic hemorrhage: This condition occurs when there is bleeding between the placenta and the uterus. It can cause vaginal bleeding and may be associated with an increased risk of miscarriage.

Molar pregnancy: A rare condition where the placenta becomes abnormal and can cause vaginal bleeding, often accompanied by other symptoms such as excessive uterine size or severe morning sickness. It is crucial to diagnose because it can lead to complications such as gestational trophoblastic disease.
Placenta previa: Although more common in later pregnancy, placenta previa can occasionally present with vaginal bleeding in the first trimester. It is essential to diagnose to prevent severe bleeding and plan appropriate management.
Uterine rupture: Extremely rare in early pregnancy but can occur in women with a history of uterine surgery, such as a cesarean section. It is a life-threatening emergency.

Cervical polyps or other cervical lesions: These can cause vaginal bleeding during pregnancy due to the increased blood flow and sensitivity of the cervix.
Vaginal or vulvar lesions: Rarely, vaginal bleeding can be caused by lesions such as varices, hemangiomas, or other vascular anomalies.
Coagulopathy: Underlying bleeding disorders can increase the risk of vaginal bleeding during pregnancy.