Maternal-fetal exchange Archives - Revista Brasileira de Ginecologia e Obstetrícia

Pregnant women may depend on the use of medications to minimize the problems caused by preexisting disease, and pregnancy itself can cause situations that compromise the maternal well-being and that require treatment. The obstetrician should be aware of the placental transfer of drugs and of fetal exposure to teratogenic or toxic agents that might compromise the development of the fetus or even its future life.Transport through the placenta involves the movement of molecules between three compartments: maternal blood, cytoplasm of the syncytiotrophoblast, and fetal blood. This movement can occur through the following mechanisms: simple diffusion, facilitated diffusion, active transport, class P, V, F and large ABC family pumps, and endocytosis. With the use of anticonvulsants the incidence of major malformations in exposed newborns is 4 to 6%, compared to 2 to 4% in the general population. Multidrug treatment is more damaging, especially when valproic acid and hydantoin are part of the combination. The recommendation for epileptic patients who have been clinically asymptomatic for two years is to discontinue the drugs they are taking. However, if seizures occur it is advisable to consult a neurologist to discuss anticonvulsant therapy with better benefits and less side effects.Local anesthetics and opioids are extensively used during the resolution of pregnancy. Lidocaine applied by the perineal route for episiotomy at a fixed dose of 400 mg presents a high concentration in maternal plasma and a high rate of placental transfer at the time of birth, with the need for caution regarding the use of repeated doses. Bupivacaine administered by the epidural route is a safe anesthetic which is present in the racemic form and has a placental transfer of about 30%. Fentanyl, an opioid anesthetic used by the epidural route in resolution of cesarean section at the fixed dose of 0.10 mg, presents high rates of placental transfer of the order of 90%, requiring caution with the use of repeated doses for analgesia during labor.