Placenta accreta spectrum

Placenta accreta spectrum is a problem with how the placenta attaches to the uterus during pregnancy. The placental cells that reach into the uterus are called trophoblasts, and in this condition they push in farther than they should, into the myometrium, the muscular wall of the uterus. That's why it's called a spectrum: they don't always go equally deep, and the condition is graded by how far they invade.

In a typical pregnancy, that invasion has a limit. During pregnancy, the inner lining of the uterus turns into the decidua, and inside it is a spongy layer where the trophoblasts stop, as if they'd hit a stop sign. Picture the roots of a plant in a pot with a mesh screen across the bottom: they grow down to the mesh and stop there. According to one of the leading theories, when the uterus has had surgery before, that spongy layer may be missing. Without the mesh, there's no stop sign, and the roots keep growing into the muscle. It's a theory, not a certainty, but it helps make sense of what's happening inside.

The most common risk factor is having had a cesarean delivery or other surgery on the uterus. And the most common complication for the mother is postpartum hemorrhage, which means heavy bleeding after giving birth.