**Core Concept**
Uterine atony refers to the failure of the uterus to contract effectively after delivery, leading to postpartum hemorrhage (PPH). This condition is a significant cause of maternal morbidity and mortality worldwide.

**Why the Correct Answer is Right**
In this scenario, the patient's uterus is soft, boggy, and enlarged, indicating uterine atony. The ineffectiveness of uterine massage and oxytocin suggests that the uterus is not contracting adequately. The next best step is to administer a uterotonic agent, specifically carboprost tromethamine (15-methyl-prostaglandin F2α), which is a potent prostaglandin analog that induces strong, sustained uterine contractions. This medication is often used in cases of severe PPH due to uterine atony.

**Why Each Wrong Option is Incorrect**
**Option A:** **Surgical Intervention (Hysterectomy)** is usually considered a last resort in the management of PPH due to uterine atony, as it carries significant long-term consequences for the patient.

**Option B:** **Methergine (Methylergonovine)** is an ergot alkaloid that can also be used to treat uterine atony, but it is not the next best step in this scenario, as carboprost tromethamine is more effective in severe cases.

**Option C:** **Massive Transfusions** may be necessary in cases of severe hemorrhage, but it is not the next best step in this scenario, as the patient is still afebrile and the bleeding is not life-threatening at this point.

**Clinical Pearl / High-Yield Fact**
In cases of uterine atony, it is essential to remember the ABCDE approach: Assess the patient's vital signs, Blood, Clotting, Disseminated intravascular coagulation (DIC), and Exsanguination. This approach helps guide management and ensures that the patient receives timely and appropriate care.

**Correct Answer:** C. Carboprost tromethamine