Threatened abortion: This is the most common cause of vaginal bleeding in early pregnancy, accounting for up to 50% of cases. The patient's symptoms of a small amount of bleeding without other complications align with this diagnosis.

Implantation bleeding: Although less common, implantation bleeding can occur around the time of expected menstruation and may be mistaken for a menstrual period. It's a possible cause given the early stage of pregnancy.
Cervical pathology: Conditions like cervical polyps or cervicitis could cause vaginal bleeding. However, these would be less directly related to the pregnancy itself.

Ectopic pregnancy: Although less likely given the early gestational age and the nature of the bleeding, ectopic pregnancy is a critical diagnosis to consider due to its potential for severe morbidity and mortality. Risk factors and further evaluation would guide the likelihood of this diagnosis.
Molar pregnancy: A molar pregnancy can cause vaginal bleeding in early pregnancy. While rare, it's a significant condition that requires prompt diagnosis and management.
Placenta previa: Though typically presenting later in pregnancy, placenta previa can occasionally cause early bleeding. It's essential to consider, especially if bleeding persists or worsens.

Ovarian torsion: While not directly related to pregnancy, ovarian torsion can cause acute pain and potentially some vaginal bleeding if there's associated ovarian cyst rupture. It's rare but requires urgent surgical intervention.
Uterine rupture (in a patient with a previous uterine scar): Extremely rare in early pregnancy but could be considered in patients with a history of uterine surgery, especially if they present with severe pain and bleeding.