**Core Concept**
Placenta increta refers to a condition where the placenta invades the myometrium, the muscular layer of the uterus, beyond the normal depth of the basal plate, but does not penetrate the serosa. This abnormal placental invasion can lead to significant bleeding during delivery.

**Why the Correct Answer is Right**
The invasion of the placenta into the myometrium is a result of the abnormal growth and differentiation of trophoblast cells, which normally invade the endometrium. In placenta increta, the trophoblast cells penetrate deeper into the myometrium, causing damage to the uterine muscle and increasing the risk of postpartum hemorrhage. The depth of invasion is crucial in differentiating between placenta increta and placenta accreta, where the invasion is even more profound.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might describe a condition where the placenta is not attached to the uterus, which is not related to placenta increta.
**Option B:** This option might describe a condition where the placenta is attached too deeply, but it does not specify the invasion of the myometrium, which is a key feature of placenta increta.
**Option C:** This option might describe a condition where the placenta is not normally attached to the uterus, which is not related to placenta increta.

**Clinical Pearl / High-Yield Fact**
Placenta increta is often associated with placenta accreta spectrum disorders (PASD), which also include placenta accreta and placenta percreta. These conditions are more common in women with a history of uterine surgery, multiple pregnancies, or assisted reproductive technologies.

**Correct Answer: C. Invasion of the placenta into the myometrium beyond the normal depth of the basal plate.**