Duphaston can be used as a treatment in women who have had miscarriages to try and prevent a repeat miscarriage. Typically this is done when the cause of the miscarriage is suspected to be a decreased level of progesterone. If you truly have a weak cervix, Duphaston will not help. However, given your history of two fill term large babies, it sounds almost certain that your cervix is not weak. A weak cervix is usually treated with something called a cerclage, in which your cervix is sown closed with sutures until the end of your pregnancy. Also, women with a weak cervix (usually called an incompetent cervix ) will not carry their babies to term. It is more likely that your doctor suspects that your progesterone level is low, and is therefore treating you with Duphaston.