Placenta accreta is a serious pregnancy complication where the placenta grows too deeply into the uterine wall and cannot separate normally after delivery. It occurs in roughly 1 in 600 pregnancies and is the leading cause of massive hemorrhage during childbirth. The condition has become significantly more common over recent decades, largely driven by rising cesarean delivery rates.
How the Placenta Normally Attaches
In a healthy pregnancy, the uterus builds a specialized lining called the decidua basalis at the spot where the placenta implants. This lining acts as both an anchor and a boundary. It lets the placenta connect firmly enough to exchange oxygen and nutrients with the baby, but it also contains a thin barrier layer that prevents placental tissue from burrowing too deep into the muscular wall of the uterus. When it’s time to deliver, the placenta peels cleanly away along this boundary, usually within minutes of birth.
In placenta accreta, that boundary layer is damaged or missing entirely. Without it, the placenta’s root-like cells invade directly into the uterine muscle. The placenta essentially fuses to the wall of the uterus, making normal separation impossible. When doctors or the body attempt to detach it during delivery, the result is severe, life-threatening bleeding.
Three Levels of Severity
Placenta accreta actually exists on a spectrum, and the depth of invasion determines how dangerous the condition is.
- Accreta is the most common and least severe form. The placenta attaches directly to the uterine muscle but does not grow through it.
- Increta means the placental tissue has invaded into the muscle layer itself.
- Percreta is the rarest and most dangerous form. The placenta grows completely through the uterine wall and can attach to nearby organs like the bladder or bowel.
All three are now grouped under the term “placenta accreta spectrum,” or PAS. The deeper the invasion, the higher the risk of catastrophic bleeding and the more likely a hysterectomy will be needed.
What Causes It
The core problem is damage to the uterine lining from previous surgery or procedures. Any scar on the uterus disrupts the protective boundary layer, leaving a gap where the placenta can invade during a future pregnancy. The most significant risk factor by far is a prior cesarean section, and the risk compounds with each additional C-section. A person who has had one cesarean has a modestly elevated risk, but after three or more cesareans, the likelihood of accreta rises dramatically, especially if the placenta implants over the old scar.
Other factors that scar or thin the uterine lining include surgery to remove fibroids, a prior dilation and curettage (D&C) procedure, and previous treatment for uterine abnormalities. Placenta previa, a condition where the placenta covers the cervix, also sharply increases the risk. When previa and a prior cesarean scar occur together, the combination is particularly dangerous.
Age and number of previous pregnancies also play a role, though mainly because both correlate with a higher chance of having had uterine procedures.
How It’s Detected
Placenta accreta is typically suspected during a routine mid-pregnancy ultrasound, especially in women who have known risk factors. Sonographers look for specific warning signs: irregular blood-filled spaces within the placenta (called lacunae), loss of the normal clear zone between the placenta and the uterine wall, and abnormal blood vessel patterns at the attachment site. When the ultrasound is inconclusive, an MRI can provide more detail, particularly for assessing whether the placenta has invaded through the back wall of the uterus or into neighboring organs.
Not every case is caught before delivery. Some are only discovered in the operating room when the placenta fails to detach. Prenatal detection makes an enormous difference in outcomes because it allows the medical team to prepare for the complex delivery these cases require.
The Risk of Hemorrhage
Severe bleeding is the defining danger. Up to 90% of women with placenta accreta spectrum need a blood transfusion, and about 40% require a massive transfusion of 10 or more units of blood. When accreta occurs alongside placenta previa, median blood loss reaches around 3,500 milliliters, roughly three times the amount lost during a typical cesarean. Even without previa, median blood loss sits around 1,200 milliliters, still well above normal.
This level of hemorrhage can lead to organ damage, the need for ICU admission, and in the most severe cases, death. It is the reason the condition is treated with such urgency and why delivery is carefully planned well in advance.
What Delivery Looks Like
When placenta accreta is diagnosed before birth, delivery is scheduled early, typically between 34 and 37 weeks of pregnancy, to reduce the chance of going into labor spontaneously. Unplanned labor or bleeding episodes can make the situation far more dangerous.
The standard approach is a cesarean delivery followed immediately by a hysterectomy, with the placenta left in place rather than removed. Attempting to pull the placenta off the uterine wall causes the worst bleeding, so surgeons deliver the baby through an incision that avoids the placenta, then remove the entire uterus with the placenta still attached. This operation is performed by a multidisciplinary team that typically includes maternal-fetal medicine specialists, surgeons, anesthesiologists, and a blood bank team standing by.
For women who strongly wish to preserve their uterus and have a less severe form of accreta, conservative management is sometimes attempted. This can involve leaving part of the placenta in place and allowing the body to reabsorb it over weeks to months, sometimes with medication to speed the process. This approach carries its own risks, including delayed hemorrhage, infection, and the possibility that a hysterectomy will still be needed. It is generally reserved for carefully selected cases at experienced centers.
Effects on the Baby
Because delivery is scheduled early to protect the mother, babies born from accreta pregnancies face the typical risks of prematurity: underdeveloped lungs, difficulty feeding, and the need for time in a neonatal intensive care unit. In one large study, about 46% of infants born to mothers with placenta accreta had low birth weight. Most of these babies do well with appropriate neonatal support, but the early delivery is a trade-off that the medical team weighs carefully when choosing the timing.
Recovery and Long-Term Outlook
Recovery depends heavily on the severity of the case and whether a hysterectomy was performed. Women who undergo a planned cesarean hysterectomy with a well-prepared surgical team generally recover over several weeks, though the hospital stay is longer than a standard cesarean, often a week or more. Blood loss and transfusion needs can extend recovery time and cause prolonged fatigue.
A hysterectomy means future pregnancies are not possible, which can be emotionally devastating for someone who wanted more children. For those who undergo conservative treatment and keep their uterus, future pregnancies carry a high risk of accreta recurring, and close monitoring is essential from the earliest weeks.
The psychological impact of the experience is significant. Many women describe feeling blindsided by the severity of the condition, especially if the diagnosis came late. Grief over loss of fertility, trauma from emergency surgery, and anxiety during subsequent pregnancies (when applicable) are all common and worth addressing with professional support.