1. Respiratory exchange and supply of nutrients to the foetus;Hytten,1963
2. Placental respiratory gas exchange and fetal oxygenation;Meschia,1989
3. Placental transfer;Stacey,1991
4. Maternal respiratory changes during pregnancy and parturition;Bonica,1973
5. Principles and Practice of Obstetric Analgesia and Anesthesia;Bonica,1967