sleep positions for preggies

Preggie women are not advisable to sleep on their back because the weight of bb will be resting on the vena cava which is the blood vessel that brings oxygen to mother's heart (think so). So if the vena being squeezed, then there might be less oxygen n blood going to our baby and our own blood circulation might be poor. Some preggies get giddy if they lie on their back. But my doctor said any position also can. I think as long as not giddy can liao. I come across some articles advising preggies try to sleep on their left, which is the best position for both mummy and baby.