There are many reasons for abdominal pain during pregnancy in addition to vaginal bleeding.
Those related to pregnancy include miscarriage (paroxysmal lower abdominal or lower back pain), ruptured tubal pregnancy, abdominal pregnancy, staphyloma (vaginal bleeding may be preceded by paroxysmal lower abdominal pain and manifested as acute abdominal pain in the event of twisted or ruptured ovarian flavinised cysts), placental abruption, etc.
Those not related to pregnancy such as pain due to cancer pain, inflammation, trauma, etc.