Perinatal Pharmacology

Introduction & scope

• Definition — Perinatal pharmacology is the study of drug disposition and drug action across the maternal–placental–fetal unit and through the neonatal transition.
• Why a separate discipline — the principles are unchanged; the physiological context is not. A pregnant woman (plasma volume +40%, cardiac output +50%) and a maturing infant are neither "small adults" nor "adults plus a passenger". Kinetics are well mapped; pharmacodynamic data remain grossly incomplete for both fetus and neonate.
• The therapeutic-orphan problem — the pregnant woman is "the last true therapeutic orphan"; Shirkey's 1968 editorial said the same of children. Laws written after therapeutic disasters excluded both groups from study, so pregnant women are systematically left untreated — the risk of the untreated disease rarely weighed.
• Counselling anchors — background risk of abnormality ~3%; fewer than 30 proven human teratogens; drugs cause only 4–5% of anomalies (~90% genetic) but are the one preventable group. Reflexive avoidance harms — stopping SSRIs caused serious morbidity, and untreated gestational hypertension itself raises malformation rates.