Delayed conception not showing heartbeat

Hi, my LMP is 16/08/2018. Yesterday I went for my first scan shows following findings : single intrauterine pregnancy,CRL O.46cm 6wk 1 day, Yolk sac measures 0.20cms,chorionic reaction is good,corpus luteum seen in the left ovary. But heartbeats didn't detected. Sonologist said it seems late conception, fetal pole detected, asked to repeat the usg 1 week later. I had a history of threatened abortion in this may 10.2wks pregnancy. And both the pregnancies are natural. I am taking folic acid prior to conception also. But I am scared and too much tensed, whether this will a valid pregnancy or a one more misscariage. Pl guide. Should I wait? What precautions, medicine shall I take now? My gynec prescribed duphaston 10 mg bd for 15 days on a day before yesterday when I went for my first check up. Pl guide me right path I am really scared , upset and tensed.