A little bit of blood in the underwear in the third trimester of pregnancy may be a preeclampsia, or cervical inflammation or cervical polyps. In the case of this kind of bleeding during pregnancy, you should go to the hospital in time for examination, first of all, to exclude the possibility of preeclampsia. If the ultrasound examination determines that there is a preeclampsia, you can choose medication for fertility preservation treatment under the guidance of the doctor. During the period of fertility preservation treatment, it is best to have absolute bed rest, and at the same time, eat more coarse fiber food and keep the bowel movement smooth. If there is no abnormality in ultrasound examination, you can do cervical examination. If there is cervicitis or cervical polyps, a small amount of vaginal bleeding may also occur. If you have cervicitis or cervical polyps during pregnancy, you can leave them untreated for a while. After delivery, intravaginal medication can be used to treat cervicitis, and cervical polyps can be removed.