I just had my baby last month and actually I was on Duphaston for the first three months. My gynac said it helps with progesterone levels to keep baby safe, so dont worry if your doctor has given it to you.
My gynac prescribed it to me in early pregnancy because of some spotting. I took it exactly as told and everything went fine, but definitely ask your doctor about your case. I never take any medicine without asking my doc first.
Honestly doc suggested me this during my first trimester so I took it without any doubts. I was too busy craving piping hot samosas and dealing with morning sickness anyway, so trusted the gynac blindly! Just check with your doc once for your own peace of mind.
For me it was a savior, doctor gave it to support my pregnancy early on. I took it till 12 weeks and went on to have a healthy normal delivery later. Trust your doctor, they know best.