What is the primary function of terbutaline (Brethine) in a patient in preterm labor?

Terbutaline (Brethine) is primarily used as a tocolytic agent in patients experiencing preterm labor. Its main function is to stop uterine contractions by relaxing uterine smooth muscle. This effect is achieved because terbutaline is a beta-adrenergic agonist, which activates beta-2 adrenergic receptors in the uterus leading to muscle relaxation and a decrease in contractility. By reducing the frequency and intensity of contractions, terbutaline helps to delay labor and potentially provide more time for fetal development and for the administration of corticosteroids to enhance fetal lung maturity.

In this clinical scenario, enhancing uterine contractions, stimulating cervical dilation, or increasing fetal heart rate would not address the primary issue of preterm labor and could actually be counterproductive. The goal is to prevent premature delivery, and only option B correctly identifies the action of terbutaline in this context.