Periods delayed by 12 days and have pregnancy symptoms

Patient: My wife has missed her periods and we have done home pregnancy test on 4th day and it was negative, she has the symptoms of pregnancy like nausea, tiredness, etc. We consulted doctor on 11th day and doctor has again done the home pregnancy test this time also it was negative. Doctor has given the Norethisterone tablets of 15mg 2 times a day for 5 days. Is it fine to take the Norethisterone tablets if she is pregnant or it will harm or it will cause a abortion if she is pregnant. please suggest