Which medication is commonly used to prevent preterm labor in pregnant clients?

Nifedipine is a calcium channel blocker that plays a significant role in the management of preterm labor. By relaxing the smooth muscle of the uterus, it helps to inhibit contractions, making it effective in delaying preterm labor. This action is crucial since managing premature contractions is vital for the health of both the mother and the fetus.

In contrast, oxytocin is used to induce labor rather than prevent it. Raloxifene is primarily a selective estrogen receptor modulator used in the treatment of osteoporosis and breast cancer, and it does not have applications related to preterm labor. Clomiphene is typically used for inducing ovulation and is not indicated for managing labor issues. Thus, nifedipine stands out as the appropriate choice for preventing preterm labor in pregnant clients.