Women experience as many symptoms of anxiety, depression, and stress during pregnancy as in the postnatal period. This can affect not only the woman herself but also the development of her fetus, and have long-term effects on several different outcomes including the cognitive ability and behaviour of her child, although most children are not affected. The particular outcomes affected may depend on the timing of the exposure, specific genetic vulnerabilities, and the quality of postnatal care provided. Recent research has shown that increased maternal anxiety is associated with altered placental function, and a greater association between maternal and fetal cortisol. This interrelationship of hormonal associations during the fetal stage could potentially impact on fetal/infant outcomes, and supports the need for continuing research in the field. Chapter 3 covers studies on maternal mood in pregnancy and explores the underlying mechanisms and types of stress.