If it is not infection, it can be mucous plug. However, when the mucous plug gets dislodged, usually it is mixed with blood. It is called as show which indicates imminent labour. If at 30 weeks pregnancy, you are having a show, please get ultrasonography done to find out whether the mouth of the uterus (cervix) has started opening up prematurely - what we call as incompetent os. If so, your Obstetrician will advise you to get the mouth of the uterus tightened by a stitch. If so, please get it done. This stitch will prevent the opening of cervix and will help to take the pregnancy as near term as possible. Just before the labour or even in very early labour pains, this stitch can be removed very easily and quickly allowing vaginal delivery. Did you have any trauma during your last delivery? Or was your previous delivery a forceps delivery? Or had you undergone Dilatation and Curettage surgery? In such cases such incompetent os can happen. I hope you have got the answer to your query with proper guidance also. For any further information, you can ask me direct question.