**Core Concept**
Uterine atony and postpartum hemorrhage (PPH) are potential complications following delivery. In this scenario, the retained placenta is a risk factor for uterine atony, which occurs when the uterus fails to contract and compress the blood vessels, leading to excessive bleeding.

**Why the Correct Answer is Right**
Forceful traction on the umbilical cord can cause uterine atony by disrupting the normal physiological process of uterine contraction. The uterus relies on the release of oxytocin and prostaglandins to contract and control bleeding. Forceful traction can interfere with this process, leading to inadequate uterine contraction and PPH. This complication can be life-threatening if not promptly managed.

**Why Each Wrong Option is Incorrect**
**Option A:** Uterine rupture is a possible complication, but it is not the most common complication associated with forceful traction of the cord. Uterine rupture typically occurs due to other factors such as previous uterine surgery or a history of uterine anomalies.

**Option B:** Placenta accreta is a condition where the placenta invades the uterine wall, but it is not directly related to forceful traction of the cord. Placenta accreta is often associated with a history of cesarean section and other uterine abnormalities.

**Option C:** Hematoma formation is a possible complication of uterine trauma, but it is not the most common complication associated with forceful traction of the cord.

**Option D:** Abdominal wall hematoma is not directly related to forceful traction of the cord. Abdominal wall hematoma can occur due to other factors such as trauma or anticoagulation therapy.

**Clinical Pearl / High-Yield Fact**
Uterine atony is a common complication following delivery, particularly in the presence of retained placenta. Prompt management of uterine atony with uterotonic agents such as oxytocin or carboprost is essential to prevent PPH.

**Correct Answer: B. Placenta accreta is a condition where the placenta invades the uterine wall, but it is not directly related to forceful traction of the cord. Placenta accreta is often associated with a history of cesarean section and other uterine abnormalities.