Intense exercise while pregnant (5.5 weeks)

I exercise about 4/days a week before I got pregnant. I would run 2 miles or elliptical, take a yoga class, lift weights, etc. I use to take an occasional spin class. Now that I'm pregnant I noticed my heart rate goes up very quickly! Around 150 BPM when it would normally be 120s-130s. I want to take a spin class tonight because they're so fun & I feel great! Should I continue working out since I feel great? Or should I tone it down until I have first Ultrasound (3/30) 

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