Placenta Accreta Spectrum

What happens in placenta accreta spectrum

Normally the placenta attaches to a specialized layer of the uterine lining (the decidua), which allows it to separate cleanly after birth. When this layer is damaged or missing, often because of a scar from previous surgery, placental tissue invades the muscle of the uterus.

When delivery comes, the placenta cannot separate, and trying to remove it can tear blood vessels and cause massive bleeding.

Risk factors

• Previous cesarean delivery: the most important risk, rising with each cesarean
• Placenta previa: a placenta covering or near the cervix. With a previa, the risk of accreta increases sharply with the number of prior cesareans, from a few percent after one to a large proportion after three or more
• Other uterine surgery: myomectomy, endometrial ablation, repeated dilation and curettage
• Asherman syndrome (scarring inside the uterus)
• IVF pregnancy
• Maternal age over 35
• Having had several previous births
• A pregnancy implanted in a cesarean scar

Symptoms

Placenta accreta often causes no symptoms during pregnancy. Some people have:

• vaginal bleeding in the third trimester, often with placenta previa
• blood in the urine if the placenta has grown into the bladder (percreta)
• pain if the uterus is weakened, rarely

Diagnosis

Early diagnosis is the most important factor in a safe outcome.

• Ultrasound: a detailed scan, usually in the second trimester, by an experienced sonographer. Signs include loss of the clear zone between placenta and uterine wall, many irregular blood spaces (lacunae) in the placenta, thinning of the uterine wall, and abnormal blood vessels toward the bladder on Doppler.
• MRI: helps when ultrasound is unclear or to map the extent of invasion, especially toward the bladder or sides of the uterus.
• Final diagnosis is made at delivery and confirmed by examining the uterus and placenta.

People with a previous cesarean should have the placental location checked carefully in pregnancy, including in early scans to look for a cesarean scar pregnancy.

Management and delivery

Planning

• care at a center with expertise in placenta accreta: maternal-fetal medicine, experienced pelvic surgeons, anesthesia, interventional radiology, urology, a blood bank able to provide large transfusions, and neonatal intensive care
• regular monitoring during pregnancy
• avoiding anemia with iron supplementation
• a clear plan for what to do if bleeding starts early, such as living near the hospital

Delivery

• Timing: planned cesarean delivery is usually recommended at about 34 to 35 6/7 weeks to balance the risks to the baby of early birth against the risk of emergency bleeding. Steroids may be given for the baby's lungs.
• Cesarean hysterectomy: the most common approach. The baby is delivered through an incision away from the placenta, and the uterus is removed with the placenta left in place, reducing blood loss.
• Additional measures: blood transfusion, balloons placed in blood vessels by interventional radiology in some centers, and ureteral stents to protect the ureters.
• Uterus-preserving approaches: in selected cases, the placenta is left in place to be reabsorbed over months, or the affected part of the uterus is removed. These carry risks of infection and delayed bleeding and are done only in experienced centers.

Complications

• massive bleeding (postpartum hemorrhage) requiring transfusion
• disseminated intravascular coagulation (a clotting disorder)
• injury to the bladder, ureters or bowel
• infection and blood clots
• ICU admission
• loss of fertility after hysterectomy
• preterm birth complications for the baby

With planned care at an experienced center, outcomes are much better than with an unexpected diagnosis at delivery.

Reducing the risk

• avoiding cesareans that are not medically needed, and considering vaginal birth after cesarean (VBAC) when suitable
• early ultrasound in pregnancies after a cesarean to detect scar pregnancies

Frequently asked questions

What is placenta accreta?

Placenta accreta is a condition where the placenta grows too deeply into the uterine wall and cannot detach after birth. This can cause severe bleeding. Deeper forms are called placenta increta and percreta.

What causes placenta accreta?

It is usually caused by scarring of the uterine lining from previous surgery, especially cesarean deliveries. The risk is highest when the placenta lies low over a cesarean scar (placenta previa). IVF, older maternal age and other uterine surgery also increase risk.

Can placenta accreta be detected before birth?

Often, yes. A detailed ultrasound by an experienced specialist can detect most cases, and MRI can help. Early diagnosis allows a planned delivery at a specialist center, which greatly improves safety.

Do you always need a hysterectomy with placenta accreta?

Not always, but a cesarean hysterectomy is the most common and safest approach for many people. In selected cases, experienced centers may try to preserve the uterus. Options depend on the depth of invasion and your wishes about future pregnancies.

When is a baby delivered with placenta accreta?

Most planned deliveries happen between about 34 and 36 weeks by cesarean section. Delivery may happen sooner if bleeding, labor or other complications occur.