Heart beat irregular?

I had some bleeding this morning. Wasn't spotting but wasn't miscarriage bleeding. Went for an ultrasound, and they told me the heart rate was 124. And measured me at 8 weeks. I thought I was 7 weeks 5 days. But the OB nurse just called and said they said the baby's heart beat was irregular. She said maybe it's because I'm still early? But 124 doesn't seem low to her. My husband carried a chromosome balanced translocation. We have a 4 year old girl, and had 3 losses. I'm stressing out!