Currently (26 weeks) between 3 and 5 bodybalance classes a week, sone treadmill walking (but that's boring!), an aquagym class and a yoga session.
At 6 weeks I was probably still doing my full exercise load, I only dropped jump around aerobics/weights when I told my instructors at the gym which was shortly after I found out (cos they told me to), dropped running for walking at 20 weeks.
I did do a disgusting amount of exercise prepregnancy though...I felt knackered but better after exercise, particularly bodybalance which us why I've replaced most of my classes with that. Used to do 2 a week or on rare occasions 3.
Everyone's different though and you definitely shouldn't push yourself if all you want to do is sleep. If I feel particularly tired I'll skip a day and not feel guilty!
Walking and swimming are fine all the way through. Cycling is okay as long as bump permits!
Running is fine to 20 weeks.
Yoga is up to your instructor, some say avoid during the first trimester, others give modified positions. Likewise pilates. Otherwise you can dk them to the end (with bump modifications!).
Step/bodypump/classes targeting abs aren't generally recommended although they can be adapted by instructors who know what they're doing. They'll err on the side of caution though, which is good.
What did you used to do?