The most common clinical cause of a pain in the belly during a new pregnancy is a preterm miscarriage. Insufficient progesterone or trauma can lead to symptoms of preterm abortion, which is caused by contractions of the uterus and a pain in the belly. It is recommended to combine the ultrasound results with the blood HCG and progesterone results and then give the appropriate clinical treatment. In addition, this condition may also occur due to the enlarged uterus pulling on the ligaments and causing a pain in the small abdomen. This pain is often mild and will be relieved naturally after a period of time. It is recommended to rest in bed and to watch for vaginal bleeding. If there is vaginal bleeding, go to the hospital for examination.