[Prolonged pregnancy: pathophysiology and clinical aspects]

The postdate pregnancy remains an unresolved clinical problem with the threat of medicolegal consequences in cases of unfavorable outcome. Placental dysfunction leading to fetal hypoxia may develop in these pregnancies at any time and for the truly postmature fetus there is a considerable risk of asphyxia. Fetal hypoxia, accompanied with hemoconcentration due to a maternofetal fluid imbalance, leads to diminished fetal urine production and a reduced amniotic fluid volume, which can cause cord compression. According to this simplified pathophysiological cascade, the monitoring of postdate pregnancies should be based mainly on ultrasound assessment of amniotic fluid volume and cardiotocography. At our institution, instead of an obligatory induction of labor at a fixed gestational age, induction is performed when the largest amniotic fluid pocket measures less than 3 cm (vertical) or when variable decelerations of the fetal heart rate appear. A nonreactive nonstress test calls for a complete biophysical profile. As long as these monitoring techniques indicate fetal well-being, pregnancy is allowed to continue, especially in the presence of an incompatible condition of the cervix.