Ultrasound for predicting placenta accreta spectrum

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According to a recent study published in the American Journal of Obstetrics and Gynecology, transvaginal ultrasound examination supports prenatal management and surgical outcome prediction in patient with past cesarean delivery (CD).

Maternal complication risk at birth and hemorrhagic morbidity risk can be reduced in patients with high placenta accreta spectrum (PAS) risk through identification in the prenatal stage. Currently, ultrasound is the main tool for screening patients with high-risk PAS at delivery.

CD rates in the United States rose from 5% in 1970 to 23% in 1993. A CD was reported in 21.1% of pregnant patients across 154 countries in a study analyzing live births from 2010 to 2018, with a prediction made that the rate of CD would be 28.5% by 2030.

PAS risk is increased in pregnancies with a history of CD, and about 95% of patients with PAS at birth present with a low-lying placenta or placenta previa. A standardized scanning program may reduce adverse outcomes in patients at highrisk of PAS.

To determine how transvaginal sonography (TVS) examination of the lower uterine segment (LUS) impacts prenatal evaluation and surgical outcomes, investigators conducted a retrospective analysis of data from Cairo University Hospital, Giza, Egypt, and University College Hospitals, London, United Kingdom from September 2019 to September 2022.

Participants included patients with a singleton pregnancy at 32 to 36 weeks of gestation, a history of 1 or more CD, and a prenatal diagnosis of an anterior low-lying placenta or placenta previa. Patient management was performed by an expert specialist multidisciplinary team.

PAS diagnosis was determined by the presence of at least 1 placental cotyledon unable to be digitally separated from the uterine wall during delivery.Diagnosis confirmation was accomplished through sample collection at the placenta-uterine interface of unusually attached areas.

At least 1 thorough TVS and transabdominal sonography (TAS) evaluation of the pelvis, placenta, and LUS was performed in all patients. Low lying placenta was defined as when both TAS and TVS examination recorded the edge as 0.5 cm to 2 cmfrom the internal os of the uterine cervix. Placenta under 0.5 cm from the internal os was defined as placenta previa.

Two experienced operators jointly reviewed ultrasound images presented anonymously, judging the risk of PAS at birth and predicting the main surgical outcome. Measurements were also performed for residual myometrial thickness, being measured with a full bladder for TAS and at the thinnest site for TVS.

There were 111 pregnant patients in the final analysis, of which 70 had 3 or more CDs. Abnormal placental tissue attachment at birth was found in 76 patients, 11 of which had superficial villous attachment and 65 had deep villous attachment. Patients with PAS had a hysterectomy rate of 78% and those with no evidence of PAS at birth 37%.

Significant variations in placental location distribution were found between TAS and TVS examinations, with 21.6% of cases reported as low lying after TAS compared to 9% after TVS. All TAS cases presented with loss of clear zone and myometrial thinning, and 48.6% of TAS cases presented with placental bulge.

For TVS cases, 23.4% presented with thin LUSs and 27.9% with very thin LUSs. Increased subplacental vascularity was also found in 54.1% of TVS cases compared to 42.3% of TAS cases. However, lacuna score distribution did not differ between the 2 methods of examination.

PAS presence at birth was more commonly seen in TAS cases with placental bulge, increased subplacental vascularity, or placental lacunae presence. All cases with increased subplacental vascularity and bridging vesselspresented with PAS at birth, along with all with a high lacuna score.

Structural changes to the cervix such as partial loss of the anterior proximal endocervix for TVS cases were significantly linked to PAS when associated with increased cervical vascularity. Of patients classified as high risk of PAS from TAS examination, 95% presented with PAS at birth.

Overall, transvaginal ultrasound examination successfully predicted PAS, allowing for improved prenatal management and surgical outcome prediction. Investigators recommended including transvaginal ultrasound examination in clinical protocols for patients at risk of complex CD.

Reference

Jauniaux E, Hussein AM, Thabet MM, Elbarmelgy RM, Elbarmelgy EA, Jurkovic D. The role of transvaginal ultrasound in the third-trimester evaluation of patients at high risk of placenta accreta spectrum at birth. American Journal of Obstetric and Gynecology. 2023. doi:10.1016/j.ajog.2023.05.004