This volume examines the role of steroids and peptides in the regulation of pregnancy and pregnancy outcome, and their long-term effects including possible influences on adult-onset diseases. During pregnancy the placenta acts as a central regulator and coordinator of maternal and fetal physiology, and the onset of labor, through its production and regulation of steroids and peptides. Perturbations to this regulatory system can result in poor pregnancy outcome, such as preterm birth and low birth weight. These in turn are linked to diseases in later life. Intriguingly, many of these regulatory actions of steroids and peptides also occur in the brain. The induction and suppression of peptides by steroids appears to be key to regulatory function in both brain and placenta. These interweaving strands, linking basic science with obstetrics, are all reviewed in depth here producing a fascinating account of an important area of materno-fetal medicine.