Supine exercises during pregnancy
From the second trimester you may feel light headed, tingling in the legs or general discomfort when you lie on your back.
This is due to the weight of the baby pressing on your vena cava which is the main vein that carries blood back to the heart from the lower body.
If this is the case for you when you do a supine exercise like a dumbbell chest press or dumbbell chest flys you may not need to stop doing them. Try increasing the angle of the bench so it's on a slight incline and this should hopefully help your symptoms.