threatened miscarriage


I had a missed miscarriage in March. im pregnant again but the doctor is saying im in a threatened miscarriage. because.... my first sonogram was at 6 weeks- 115 BPM, 7 weeks-97 BPM, 7 weeks 3 days- 129 BPM. i go back to 8 weeks to check again.... anybody go through anything similar? theyre telling me expect the worst so i obviously do.