Pregnancy 10 week

Patient: Hi, My wife is 10 week pregnant and it is her first pregnancy. Two days back she was having pain in lower back. We talked to our Gynae, she told to take Duphaston 10 mg, twice a day along with a paracetamol 500 mg. My wife is already having susten 200 since the pregnancy was confirmed. All her reports till now is normal. Kindly tell me the use of duphaston and why it was given along with susten 200. Thnx