What could be the possible cause of habitual abortion in a woman who is below thirty of age, not obese, not hypertensive, and did every precaution she needs to keep her pregnancy, did circulage, took Duphaston and cyclogest suppository (supplementary progesterone hormone) with IM injection of progesterone continuous till 6 months of pregnancy together with regular use of heparin to prevent coagulation and risk of an antiphospholipid problem although it is negative with continuous rest, then all of the sudden, the baby died in utero and get the abortion.

this case has repeated several times to several women without possible explanations?

Could anyone can help us resolve this problem?