Hi Kathy! Congratulations on your pregnancy.
When starting back into your exercise program, you need to come back slowly and at half the intensity. Start out with only three short non-consecutive cardio workouts and modify the intensity of those workouts so that you stay in the lower end of your training zone(NOTE: when pregnant you should never train in the high end of your training zone, rather stay in the middle).
If you were weight training before you quit exercising, cut back to very light weight for a few weeks and allow your body to get acclimated once again. Now that you are at 16 weeks, you should avoid doing any weight training exercises flat on your back, but rather on an incline.
After about three weeks of this "initiation" period, you can gradually work your way back to what you were doing right before you quit(with the exception of doing anything flat on your back). Keep in mind that your goals should be to cautiously obtain and maintain the level of fitness that you had just before you had to quit. Never push to become super fit while pregnant.
As the weeks progress, you will need to adjust your workouts to accomodate your physical changes (ex: take impact out of moves to discourage unnecessary pressure on the pelvic floor.)
Important things to remember:
1) Stay VERY hydrated at all times, especially during exercise.
2) Take your fitness program day by day and modify on a "workout-to-workout" basis.
3) Discontinue exercising if you feel pain or discomfort.
4) Let your doctor know about your exercise program.
Good Luck with everything!
