If there are signs of miscarriage in the 40th day of pregnancy, with stomach pain and vaginal bleeding, it is usually due to insufficient production of progesterone and can manifest as a miscarriage. In this case, an ultrasound should be performed to confirm intrauterine pregnancy, followed by a blood test for progesterone. If the progesterone level is low, you should promptly take dydrogesterone or progesterone for supplementation, which can have the effect of preserving the pregnancy. You should also pay attention to bed rest, not to exercise strenuously, and try to relax and not to be too nervous. If there are signs of miscarriage, but no gestational sac is detected during the ultrasound, it is not possible to keep the pregnancy. You should pay attention to the size of the bleeding and the specific situation of stomach pain, exclude ectopic pregnancy in time, and only keep the pregnancy if it is confirmed to be intrauterine.