The same abdominal pain differential as non-pregnant patients, plus:
Ectopic pregnancy
First trimester abortion
Complete abortion
Threatened abortion
Inevitable abortion
Incomplete abortion
Missed abortion
Septic abortion
Round ligament stretching
Incarcerated uterus
Malposition of the uterus
Complete abortion
Threatened abortion
Inevitable abortion
Incomplete abortion
Missed abortion
Septic abortion
Labor/Preterm labor
Placental abruption<unk> 
Vasa previa
Uterine rupture
Vaginal trauma
HELLP syndrome
Cholestasis of pregnancy
Chorioamnionitis
Incarcerated uterus
Acute fatty liver of pregnancy
Malposition of the uterus
Placenta accreta
Placenta increta
Placenta percreta
Hemorrhagic ovarian cyst
Fibroid degeneration or torsion
Ovarian torsion
Constipation
Placenta previa
The same abdominal pain differential as non-pregnant patients, plus:
Vasa previa
Ectopic pregnancy
Placenta accreta
First trimester abortion
Septic abortion
Complete abortion