Exercise Guidelines by TrimesterThese basic training guidelines are good to follow during each trimester:First Trimester The first trimester is very taxing on your body. Critical development is tak-ing place, so it is important to not overexert yourself or get overheated. You may experience a high degree of fatigue and nausea, which will limit your activity and determine how far you should go. For beginners, start slow with regular walking and build intensity as your comfort level allows.