**Core Concept**
Vaginal delivery is a mode of childbirth where a baby is born through the birth canal. It is a preferred method of delivery for most women, but certain conditions may necessitate a cesarean section. The decision to allow vaginal delivery is based on the presence of certain risk factors or complications.

**Why the Correct Answer is Right**
The correct answer involves conditions that are associated with an increased risk of complications during vaginal delivery. These conditions require a more controlled and safe environment, which can be provided by a cesarean section. For example, a previous cesarean section or a placenta previa may increase the risk of bleeding or other complications during vaginal delivery.

**Why Each Wrong Option is Incorrect**
**Option A:** **Bicornuate Uterus** - A bicornuate uterus is a congenital anomaly where the uterus is divided into two separate horns. While it may increase the risk of preterm labor or fetal growth restriction, vaginal delivery is generally possible with proper management.

**Option B:** **Placenta Previa** - Placenta previa is a condition where the placenta partially or completely covers the cervix. While it is a contraindication for vaginal delivery, the correct answer is not placenta previa.

**Option C:** **Previous Cesarean Section** - A previous cesarean section is a contraindication for vaginal delivery in the case of a classical cesarean section, but it's not a blanket contraindication for all types of previous cesarean sections.

**Clinical Pearl / High-Yield Fact**
In general, vaginal delivery is allowed in women with a previous low-transverse cesarean section, but a trial of labor after cesarean (TOLAC) should be carefully planned and managed by an experienced obstetrician.

**Correct Answer:** D