Are these heartbeats the sign of twins

Sarah

I have a fetal doppler at home today picked up two different sounding heartbeats with two diffrent bmp range's I kno one could be mine but the beats bpm are both two high normal adult range is 60 to 80 bmp. The first heartbeat sound was 140 to 150 bmp and then when I moved across my lower belly the next was 110 to 120 bmp has anyone else experienced this and then been told there having twins I'm 18 weeks pregnant thanks for reading ..