1st Trimester Fitness Routine

Priyamvada
What types of exercises are okay in the first trimester? I'm feeling bad as I was used to doing some vigorous step aerobics. It's a sudden change that I am not going anywhere because of the fear if miscarriage. But this way I'd gain weight very fast. I am doing deep breathing 'Pranayama', but it ain't equivalent to cardio / strength training. Please advise!