This is the most powerful dua to prevent miscarriage.
Bismillah Illazi La Yadurru ma-asmihi Shai-Un Fill Ardi Wala Fis Samaa-e Wahu Wass-Samee-Ul Aleem
Recite this dua before sleeping 111 times during pregnancy to prevent your miscarriage. This is a very effective dua if you already have miscarriage symptoms and want to prevent it.
Thanks to Sabiha who asked this question What is the dua for miscarriage in Islam? This question has been asked many times before. This answer will not help only one person but others too to prevent miscarriage using this given dua.