When low progesterone occurs during pregnancy with a second child, it may be caused by abnormal thyroid function or endocrine abnormalities in the body, or it may be caused by insufficient luteinizing function, resulting in low progesterone. You should go to the hospital for a timely examination to determine the cause and then take symptomatic treatment. If the low progesterone is caused by abnormal thyroid function, it should be supplemented and treated in a timely manner, otherwise it will easily lead to the fetus affecting intelligence and causing mental retardation or poor development after the baby is born. Otherwise, the fetus may stop growing and developing.