What Causes Miscarriage During The Fourth Month?

Hi,my wife had two misscarriage in 2009(withen 4th month). She could not conceive in 2010. Since may 2011 she is on AKT4 and now taking Rifa i6 and Silbostin and also conceived. Whether this medication will have any complication in the pregnancy ? Her LMP was 31.5.2011. As advice by Dr, TVS was done on 5th July but from 6th evening she had brown discharge(spotting) and from 8th the spotting becomes bright red. From 10th july evening the spotting have stopped. Her abdomen size has reduce a little. During our visit to dr on 8th she advice us TVS again on 12th. Please help me out. We are confused. Before the 1st TVS was done their was no spotting except some white dischsrge. Is this spotting due to TVS?