Suggest Treatment And Causes For Blighted Ovum

I m 31yrs and had my 1st miscarriage on 22nd march 20014 (fetus was properly developed and pregnancy was for two months)and again on 15th July 20014(one month pregnancy),my us report was blighted ovum what does it means? Does I need any test to be done my la test is absent. rubella test is also ok. please suggest me what should I do ?