**Core Concept**
In placenta previa, the placenta partially or completely covers the internal cervical os, posing significant risks to both the mother and the fetus. The condition can lead to various complications due to the abnormal implantation of the placenta.

**Why the Correct Answer is Right**
Rapid dilation of the cervix (C) is not typically associated with placenta previa. In fact, the cervix may be firm and closed due to the placenta's covering of the os. This is in contrast to other conditions, such as preterm labor, where cervical dilation is a common symptom. The abnormal implantation of the placenta can lead to painless vaginal bleeding, which can cause maternal shock and fetal distress.

**Why Each Wrong Option is Incorrect**
**Option A:** Malpresentation can be a complication of placenta previa, as the abnormal implantation of the placenta may lead to an increased risk of umbilical cord compression or prolapse, resulting in malpresentation.

**Option B:** Premature labor is indeed a complication of placenta previa, as the condition can cause maternal bleeding, which can lead to fetal distress and subsequent preterm labor.

**Option D:** Retained placenta is also a potential complication of placenta previa. The abnormal implantation of the placenta may lead to difficulty during delivery, resulting in retained placental tissue.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that placenta previa is a clinical diagnosis that can be confirmed by ultrasound, and it's crucial to avoid digital vaginal examination, as it can exacerbate bleeding.

**✓ Correct Answer: C. Rapid dilation of cervix**