ABSTRACT
This chapter describes the transfer of placenta. The main functions of the placenta are gas exchange, nutrient and waste exchange, transfer of immune complexes and hormone synthesis. Placental transfer is subject to exactly the same rules governing transfer of substances across all semi-permeable phospholipid membranes. Mechanisms of transfer include: simple diffusion; facilitated transport; secondary active transport; active transport; pinocytosis and bulk transport. The factors govern transfer across the placenta are lipid solubility, degree of ionisation, degree of protein binding, pH, molecular weight and concentration gradient across the placenta. The thiopentone crosses the placenta rapidly but the neonate does not suffer excessive sedation unless doses exceed 8 mg/kg. Pethidine is a highly lipid-soluble drug and so it passes freely across the placenta reaching equilibrium in about 6 minutes and reaching maximum levels in the fetus at around 2–3 hours.
