The placenta is usually attached to the wall of the uterus. It grows in the uterus and supplies oxygen and food to the baby via umbilical cord.
The placenta grows in the upper portion of the uterus and it stays there until birth. In the last stage of labor, the placenta detaches itself from the uterus wall and gets pushed out through the birth canal (afterbirth).
When the placenta is attached too deep into the uterine wall without penetrating the muscles of the uterus, then it is termed as placenta accreta. It is reported that the incidence of placenta accreta has increased to 3 out of 1,000 cases during the past decades compared to about 0.8 cases out of 1,000 in 1980.
Deepness and Severity
In about 1 of 2,500 pregnancies, the placenta is attached too deeply into the uterus. Depending on the placenta’s depth of attachment and the severity of the condition, we categorize the conditions as placenta accreta, placenta increta or placenta percreta.
Compared to placenta accreta, in placenta increta, the placenta is attached even deeper into the uterine wall. However, it does not penetrate the uterus muscles. Of all the cases reported, placenta increta is found in about 15% of the cases.
Placenta percreta happens when the placenta goes further into the uterus muscles and attaches itself to other organs, for example, the urinary bladder. This condition is least common and accounts for about 5% of all cases.
Causes and Symptoms
Though the exact cause of placenta accreta is not known, the condition could be associated with (i) previous cesarean deliveries and (ii) placenta previa.
There is a greater likelihood of placenta accreta in the future with cesarean delivery. With the increase in cesarean deliveries, the possibility of placenta accreta also increases. In more than 60% of cases with placenta accreta, the cause was found to be multiple cesareans.
In some women, the placenta is present in the lower portion of the uterus, covering the cervix totally or partially—placenta previa. During the third trimester, 1 among 200 pregnant women is affected by placenta previa and 5–10% of women with placenta previa have placenta accreta.
The risk of placenta accreta increases with previous surgery in the uterus, The more the uterine surgeries, the more risk . Pregnant women over 35 years are more prone to placenta accreta. The risk increases each time a woman gives birth. When there are abnormalities in the uterus or scars in the tissues lining the uterus, the risk increases.
Risks are also associated with:
- uterine irradiation
- uterine curettage
- uterine leiomyomata
- hypertensive disorders of pregnancy
- endometrial ablation
- Asherman’s syndrome
Often placenta accreta is asymptotic. A warning sign for placenta accreta is bleeding in the third trimester.
Complications for Baby and Mother
Placenta accreta leads to premature delivery. The baby will face successive complications that are associated with premature delivery.
For the mother, the main concern is hemorrhaging, which may become severe. The bleeding could result in adult respiratory distress syndrome (lung failure), disseminated intravascular coagulopathy (ab normal blood clotting) and kidney failure .
With placenta accreta, it is difficult for the placenta to separate from the uterine wall. During the placental detachment stage of labor, damage can be caused to organs such as uterus, bowel, and bladder. Postoperative bleeding may require surgery. Other complications include:
- postoperative thromboembolism
- multisystem organ failure
- amniotic fluid embolism
- electrolyte abnormalities
- maternal death
Even though the exact maternal mortality rate associated with placenta accreta is not known, reports suggest a rate of 6–7%.
Diagnosis and Treatment
Transabdominal ultrasound and transvaginal ultrasound are used for diagnosis of placenta accreta. Transvaginal ultrasound provides a more detailed view of the lower segment of the uterus. Grayscale ultrasonography diagnoses placenta accreta with a specificity of 96–98%. Sometimes magnetic resonance imaging (MRI) is also ordered. The test is safe for both the mother and the baby in the womb, and provides a clear picture of the internal body parts.
Placenta accreta cannot be prevented, and there are very few treatment options available.
Upon diagnosis, physicians observe the pregnancy and plan a cesarean delivery that may save the uterus. It is important to talk with physicians about this surgery if one is planning future pregnancies.
In severe cases of placenta accreta, a hysterectomy is recommended. This therapeutic intervention can make women unable to conceive again or lead to uterus removal.
Reviewed by Catherine Shaffer, M.Sc.
- ACOG, Placenta accreta, www.acog.org/.../Placenta-Accreta
- American Pregnancy Association, Placenta previa, http://americanpregnancy.org/pregnancy-complications/placenta-previa/
- March of Dimes, Placental accreta, increta and percreta, www.marchofdimes.org/.../placental-accreta-increta-and-percreta.aspx#
- Mayo Clinic, Placenta accreta, http://www.mayoclinic.org/diseases-conditions/placenta-accreta/basics/risk-factors/con-20035437
- Brigham Health Club, Placenta Accreta: Myths and Facts, brighamhealthhub.org/five-myths-and-facts-about-placenta-accreta
- Society for Maternal Fetal Medicine, Placenta Accreta: Myths and Facts, https://www.smfm.org/publications/103-placenta-accreta