Placenta accreta spectrum

By trimester

Weeks 1–13

1st trimester

Early pregnancy is the time to document every prior cesarean birth, myomectomy, uterine curettage, endometrial ablation, or other uterine procedure. If the placenta implants low near a scar, the obstetric team may plan targeted imaging rather than assuming an early scan can rule placenta accreta spectrum in or out.

Weeks 14–27

2nd trimester

Placental location and suspicious ultrasound signs are often assessed around the anatomy scan. A normal-looking scan lowers concern but does not erase a strong previa-and-scar risk history. If placenta accreta spectrum is suspected, referral to maternal-fetal medicine and a higher-level center should begin before bleeding or labor.

Weeks 28–birth

3rd trimester

Confirmed or strongly suspected placenta accreta spectrum requires an individualized delivery plan, blood-bank preparation, anesthesia and surgical coordination, and neonatal support. ACOG-linked guidance commonly plans cesarean birth with hysterectomy at 34 weeks through 35 weeks and 6 days in stable patients, with earlier delivery if bleeding, labor, rupture, or another complication occurs.

What does the evidence show for placenta accreta spectrum?

• Placenta accreta spectrum includes abnormal placental adherence and invasion into the uterine muscle, with the deepest forms reaching the uterine surface or nearby organs. Prior cesarean birth is the most common risk factor, and placenta previa is frequently present. 1
• The ACOG and SMFM consensus states that absent ultrasound signs do not exclude placenta accreta spectrum. Clinical risk factors remain important, and outcomes are optimized when suspected cases deliver at a level III or IV maternal-care facility before labor or bleeding with an experienced multidisciplinary team. 2
• A 2023 meta-analysis of 54 imaging studies involving 5,307 high-risk pregnancies found pooled ultrasound sensitivity of about 87% and specificity of about 86% against postnatal pathology. These estimates leave both false-negative and false-positive results and came largely from selected scar-and-previa populations. 3
• For a stable antenatal placenta accreta spectrum plan, ACOG-linked guidance recommends cesarean delivery with hysterectomy between 34 weeks and 35 weeks and 6 days at a center with an experienced team and massive-transfusion capability. The placenta is generally left in place because attempted separation can trigger severe hemorrhage. 1
• Placenta previa can present with painless vaginal bleeding in the second or third trimester and is itself a major hemorrhage risk. Because previa and accreta spectrum often overlap, any bleeding in a pregnancy with suspected accreta needs immediate obstetric assessment rather than home monitoring. 4

When should I call my provider about placenta accreta spectrum?

Any vaginal bleeding with suspected placenta accreta spectrum needs immediate obstetric assessment because placenta previa and abnormal placental attachment can produce major hemorrhage. Call emergency services for heavy bleeding, fainting, severe weakness, or severe pain. Regular contractions, fluid leakage, or reduced fetal movement also warrant urgent obstetric triage rather than waiting for the next scheduled visit. Whatever the pattern, any symptom that feels beyond your usual range is a reason to call: obstetric teams expect these questions and would rather hear early than late.