For ethical reasons, pregnant woman are not included in clinical trials so that data regarding safety and efficacy of many drugs are scarce. It is known that xenobiotics across the placental barrier but studies regarding quantity and mechanisms of this transfer remain insuffisant. Among the different methodologies to evaluate drug transfer, perfusion of human cotyledon is one of the most relevant ones. The two sides of the cotyledon, fetal and maternal ones, are perfused within the hour after delivery with EARLE medium in a double closed circuit. The studied drug (it can be any drug given to pregnant mothers) and antipyrine (the control molecule) are added at the beginning of the three hours perfusion realized at 37C, with maternal flow rate of 12ml/min and fetal one of 6ml/min. Samples are collected along the perfusion and the drugs dosage will be done in the pharmacology department of Cochin Hospital. Tissues of the cotyledon will be also collected to study the proteins, and ARNs expressed. The drug concentrations will be analyzed by calculating fetal to maternal concentrations ratios and a fetal transfer rate (fetal drug quantity on total drug quantity at the end of the perfusion). Then modelling on Monolix software will be done to estimate the transfer constants across the two compartments. Modelling will allow to estimate the interindividual variability and to test covariables like sex, gestation duration, genetics, or protein expression. Proteins will be studied by an appropriated method (western blot, or proteomic analysis). The genetics study will consist in candidate gene approach. Polymorphisms will be chosen in genes coding for transporters or enzymes or their regulators.