Which drug can be used to treat fetal supraventricular tachycardia?

Digoxin is a medication that can effectively be used to treat fetal supraventricular tachycardia (SVT). This condition involves an abnormally fast heart rate in the fetus due to an electrical issue in the heart. Digoxin works by slowing down the heart rate and improving the heart's efficiency, making it particularly beneficial in cases of SVT. It achieves this through its action on the cardiac glycosides mechanism, enhancing vagal tone and helping to restore a normal rhythm.

In the context of this question, other medications listed have different uses and are not suitable for treating fetal SVT. Pitocin is primarily used to initiate or augment labor; Betamethasone is a corticosteroid often used to promote fetal lung maturity in premature infants; and Terbutaline, a tocolytic agent, is generally used to relax the uterus and manage preterm labor but does not have a role in managing fetal heart rate abnormalities such as SVT. Therefore, Digoxin stands out as the most appropriate choice for this particular condition.