[Prematurity in multiple pregnancies].

At present, 1.5% of all pregnancies are twin pregnancies, but twin pregnancies account for 25% of all premature infants. The chorionicity plays an important role: the risk of preterm birth before 32 weeks is 5.5% in dichorial twins and almost double (9%) in monochorial twins. The rate of intrauterine growth restriction and also the perinatal mortality are twice as high in monochorial compared to dichorial twins. In cases of imminent preterm labour, tocolysis is recommended until lung maturity has been achieved. The preferred drugs, are oxytocin antagonists because of the increased cardiorespiratory strain in multiple pregnancies. Prophylactic bed rest and 'home uterine activity monitoring' have not been shown to improve the outcome, and a recent review (2005) demonstrated a twofold increase in preterm labour after cervical cerclage. In two large placebo-controlled studies, the rate of preterm delivery in high-risk singleton pregnancies was significantly reduced by the regular application of progesterone. A potential effect on multiple pregnancies is yet to be shown.