**Core Concept**
External Cephalic Version (ECV) is a manual technique used to rotate the fetus from a breech presentation to a cephalic presentation. The procedure involves a healthcare provider applying gentle pressure to the mother's abdomen to guide the fetus into a head-down position.

**Why the Correct Answer is Right**
Flexed breech, also known as frank breech, is not a contraindication for ECV. In fact, frank breech is one of the most favorable presentations for ECV, as the baby's legs are folded up towards its chest, making it easier to manipulate the fetus into a head-down position. The success rate of ECV is higher in frank breech presentations compared to other types of breech presentations.

**Why Each Wrong Option is Incorrect**
**Option A:** Twins are a contraindication for ECV because the procedure can be challenging and risky in multiple gestations. The healthcare provider may inadvertently rotate one twin while leaving the other in a breech presentation, which can lead to complications during delivery.

**Option C:** Premature rupture of membranes (PROM) is a contraindication for ECV because the procedure can cause further rupture of the membranes, leading to an increased risk of infection and other complications.

**Option D:** Previous abruption is a contraindication for ECV because the procedure can cause further uterine trauma, leading to another abruption and potentially life-threatening complications.

**Clinical Pearl / High-Yield Fact**
It's essential to note that ECV should only be performed by a trained healthcare provider in a hospital setting, as the procedure can be associated with complications, such as uterine rupture or fetal distress.

✓ Correct Answer: B. Flexed breech