My Experience: Yoga Teacher, 8 Years
Description:
Some of the Relaxation Asanas and Pranayama you could safely do are given below:

Dradhasana: The trunk pose - Lie on one side (on the left side after a meal to activate digestion also before sleeping in order to warm the body). This activates the right nostril. Keep your body in one straight line - feet, knees, thighs one on top of the other and watch your natural breath. You can make yourself comfortable using pillows to support your back, and even bend a knee and use a pillow under it for support.

Shavasana: Dead body pose - Lie on your back. Let the arms rest on the sides (keep them at a comfortable distance from the body), Make sure the feet are comfortably apart, and the palms are facing the ceiling. Try to make your back as flat against the floor as possible. Once more try to consciously relax each part of your body and breathe normally. Don’t do this pose for long periods of time after the 5th month of pregnancy. (Not more than two to three minutes).

Nishpandbhav: Sit against a wall, with your hips slightly away from the wall, the back of neck, shoulders and upper back nicely supported against the wall, legs comfortably apart, palms on thighs turned upwards, and your elbows and shoulders relaxed. Start to listen to the fading sounds. Once one sound goes, find another sound to listen to. Listen without judgment (I like or dislike this sound), without analysis (oh a crow, a plane, etc!) and without attachment (allow the sounds to come and go). Try to just be an observer, a witness. This is a simple but wonderful exercise, which allows you to relax completely.