Final answer:
Optimal fetal circulation is achieved when the mother is in the side-lying position. Lying on the back or abdomen can compress blood vessels and restrict blood flow to the fetus.
Step-by-step explanation:
Optimal fetal circulation is achieved when the mother is in the side-lying position. This position helps to improve blood flow to the placenta and the fetus. When the mother lies on her back, it can compress the vena cava, reducing blood flow to the fetus. Additionally, lying on the abdomen is not recommended during pregnancy as it can put pressure on the uterus and restrict blood flow.