Tocolysis for Acute Preterm Labor: Where Have We Been, Where Are We Now, and Where are We Going?

Tocolytics have been used for over 60 years for women with preterm labor, which ultimately can lead to preterm birth (PTB). Diagnosing preterm labor is challenging, but use of objective tests such as transvaginal ultrasound of cervical length assists in the identification of women at the highest risk for PTB. Once preterm labor has been diagnosed, clinicians can choose from a variety of drug classes (cyclooxygenase inhibitors, calcium channel blockers, and betamimetics) to achieve the primary goal of delaying delivery by 48 hours, thereby allowing time for administration of corticosteroids for fetal lung maturity, and if appropriate, starting magnesium sulfate for fetal neuroprotection. Cyclooxygenase inhibitors are the only class of tocolytics proven to decrease PTB < 37 weeks. Knowledge of the safety and effectiveness of these medications is paramount. Several additional agents (e.g., oxytocin receptor antagonists) have significant promise, but further studies are required before these medications can be approved for tocolysis in the United States. As we look into the future of tocolysis, we anticipate that deeper understanding of the complex physiology of preterm labor will allow us to uniquely target different etiologies that lead to the final path resulting in spontaneous preterm delivery.