yes there is such medicine. something like a hormone (i think it's hcg...) to send stronger signal to your womb that you are pregnant so that the system will work harder for sustaining the pregnancy.
ask your doctor. but whether s/he will prescribe depends on whether your doc. think you need the med or not, ie, whether you have signs of miscarriage.
that really depends on whether you trust your chinese doctor.... folic acid is natural. you can find in green leaves, orange... but folic acid wouldn't help much in avoiding a miscarriage.