The causes of lower left abdominal pain in pregnant women include physiological causes, pre-miscarriage, ectopic pregnancy, ovarian cyst torsion, etc. The causes can be identified under the guidance of a doctor. 1. Physiological reasons: pregnancy will increase the uterus on the surrounding ligaments will have a pulling effect, but also pressure on the pelvic floor tissues, may cause the left lower abdominal pain, the general level of pain is not serious, can be relieved after appropriate rest, this is a physiological phenomenon. 2. Pre-eclampsia: It may also cause pain in the left lower abdomen, accompanied by a small amount of vaginal bleeding, ultrasound examination is clear that the normal intrauterine pregnancy, combined with clinical manifestations, progesterone and blood HCG (human chorionic gonadotropin) test can help diagnosis. 3. Ectopic pregnancy: it can also cause vague pain in the left lower abdomen, and may be accompanied by irregular vaginal bleeding, which can be diagnosed by ultrasonography, blood HCG test and puncture of the posterior vaginal fornix. 4. Left ovarian cyst torsion: can cause persistent pain in the left lower abdomen, combined with gynecological examination, ultrasonography can help diagnosis. Clinically, when pregnant women have left lower abdominal pain, they need to go to the hospital in time to find out the cause and deal with it in time.