There is no method to prevent a threatened first trimester miscarriage from getting worse. Even bed rest is of no benefit although, conversely, riding a mountain bike over rough terrain is not advised. Many of these pregnancies are chromosomally abnormal: you don’t even want to stop them from miscarrying.
there is no drug that will correct chromosomal/DNA abnormatities in the foetus/embryo, Reseach it classically a big problem in this field because even after 3 miscarriages there is a 60% chance, whatever drug you give (read the diethylstilboestrol saga) that the pregnancy will now go to term.. Proper reseach means DNA research of the aborted pregnancy and very large group of patients who refuse to be randomised.