This should be practiced before any pranayam for at least a few minutes and we should always breath with our diaphragm for all breathing techniques. Sit in a comfortable sitting position, using the wall, a chair, cushions or bolsters as support if needed. Alternatively lie in shavasan or tadagasan. Tadagasan is useful during pregnancy as it allows the lower back to relax, however in the later stages of pregnancy sitting is preferred.
Place one hand on the belly and the other on the chest. Inhale deeply, using the diaphragm. If one is using the diaphragm then as one inhales the diaphragm will move downward, pushing the abdominal contents down and out, making the abdomen rise. On exhalation the diaphragm will move upward and the abdomen will fall. Continue the practice. This is the type of breathing we want to practice. If the chest is moving then we are still breathing shallow, without the diaphragm. If we use the diaphragm then the lower lobes of the lungs are being used, improving their efficiency and giving a positive effect to the heart, liver, stomach and intestines. It is the most natural and efficient way to breathe, however many people do not breathe in this way due to the modern lifestyle. Just by altering the way we breathe we can see huge benefits.
Breathwork India 