Blood in the 45th day of pregnancy may be caused by preeclampsia, ectopic pregnancy, cervical polyps and other reasons. 1. Pre-eclampsia: It can cause a small amount of vaginal bleeding, accompanied by paroxysmal lower abdominal pain or lumbar pain, ultrasound can clarify the normal intrauterine pregnancy, combined with progesterone and blood HCG (human chorionic gonadotropin) levels can help diagnosis. 2. Ectopic pregnancy: it is a common obstetrics and gynecology emergency abdomen, most commonly seen in tubal pregnancy, mainly manifested as a small amount of vaginal bleeding, accompanied by lower abdominal pain on one side, when the rupture of the pregnancy site can cause tearing pain in the lower abdomen, ultrasonography, blood HCG, posterior fornix puncture can be assisted in the diagnosis. 3. Cervical polyps: due to the brittle nature of polyp tissue, can cause recurrent small amounts of vaginal bleeding, not accompanied by abdominal pain, can be diagnosed through gynecological examination. When 45 days pregnant with vaginal bleeding need to go to the hospital in time to find out the cause, and actively deal with.