Preterm delivery is a public health issue of major proportion. More than 12% of deliveries in the United States that occur at less than 37 weeks gestation preterm labor (PTL) represents the largest single reason for preterm birth (PTB). Attempts to prevent PTB have been unsuccessful. This paper of maintenance tocolytic therapy will examine the efficacy and safety of the drugs, both oral and subcutaneous, which have been utilized for prolongation of pregnancy following successful arrest of a documented episode of acute preterm labor. The evidence for oral tocolytics as maintenance therapy as well as parenteral medications for such patients is offered. Finally, the effects in the United States of the Food and Drug Administration (FDA) action on such medications are reported. 1. Introduction The rate of preterm birth (PTB) defined as less than 37 weeks gestation is unacceptably high worldwide. In the US, it exceeds 12% [1]. PTB is responsible for up to 75% of infant mortality and up to 50% of long-term neurologic deficits [2]. The majority of these deliveries result from either preterm labor or preterm premature rupture of the membranes accompanied by preterm labor [3]. Acute preterm labor at 20 0/7 to 36 6/7 weeks can be successfully treated in 70–90% of patients if the diagnosis is made prior to advanced cervical dilation (≥3？cm) [4]. This success rate is not achieved if there is chorioamnionitis or placental abruption causing PTL. However, once these women are sent home following successful tocolysis, recurrent preterm labor and/or preterm premature rupture of the membranes is likely, and these patients are at high risk to deliver at <37 weeks’ gestation [5]. There are several choices of drugs for maintenance tocolysis after acute preterm labor is arrested, but some feel that treatment does not significantly prolong gestation [6]. For example, oral tocolysis with beta-agonist or with oral magnesium has been shown in randomized clinical trials not to extend gestation or benefit the neonate [5, 7]. Similarly oral nifedipine maintenance tocolysis has not been shown to be beneficial [8]. However, failure of maintenance tocolysis may have more to do with the agent and its side effects (thus compliance) than with tocolytic drug efficacy. There is also an effect of the route of delivery of the tocolytic drug on efficacy and compliance. For example, the oxytocin receptor antagonist Atosiban given parenterally and the continuous subcutaneous administration of terbutaline supplemented by daily perinatal nursing calls and home uterine activity monitoring, both
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