[header] How to do hiit workouts during pregnancy [title] Do hiit workouts during the second and third trimesters. [step] Your first trimester is not the best time to do hiit workouts. Instead, the second trimester is a good time because you start to regain energy and feel less sick. 
You can continue into the third trimester as long as you monitor how your body feels. If you get more fatigued during the last six weeks of your pregnancy, you may want to decrease the intensity.