I had 2 miscarriages at 12weeks because of no embryo formation .what's the reason y the embryo not formed.its my fault or my partners fault?

Maybe neither: Early research on fetal loss has shown as many as 1/3 will have a chromosomal defect. If the material was not studied it is hard to guess what happened. Sometimes either parent will carry a "balanced" chromosome defect that results in frequent fetal loss. After 3 many medical geneticists recommend the women get tested. You may want to contact one (children's hospitals) & discuss your concerns.