Transvaginal ultrasound accurately predicts placenta accreta spectrum risk

Transvaginal ultrasound examination may be used to improve prenatal management and prediction of surgical outcomes in patients with a prior cesarean delivery (CD), according to a recent study published in the American Journal of Obstetrics & Gynecology.

Maternal complications and hemorrhage morbidity risk are reduced in patients at high risk of placenta accreta spectrum (PAS) at birth through prenatal identification. This also allows for reduced use of massive transfusion and risk reoperation through management by an expert multidisciplinary team (MDT).

CD rates have increased from 5% to 23% in the United States between 1970 and 1993, with a recent analysis of world data indicated CD will be performed in 28.5% of births by 2030. Of patients with PAS at birth, 95% have a low-lying placenta or placenta previa and prior CD history in the prenatal period.

Standardized prenatal scanning protocols may be used to improve perinatal outcomes in patients at high risk of PAS at birth. Currently, ultrasound is the most common tool for screening high risk patients.

To determine the role of transvaginal sonography (TVS) examination of the lower uterine segment (LUS), investigators conducted a retrospective analysis of data obtained from September 2019 to September 2022. Data was collected at Cairo University Hospital, Giza, Egypt, and University College Hospitals, London, United Kingdom.

Participants presented with a singleton pregnancy at 32 to 36 weeks of gestation, had 1 or more prior CD, and were diagnosed prenatally with a placenta previa or anterior low-lying placenta. Exclusion criteria included multiple pregnancies, emergency delivery before 32 weeks of gestation, and incomplete records.

Patients received either hysterectomy or conservative management, with management performed by an MDT. An image capture digital photographic protocol was used to record intraoperative features and gross examination of the hysterectomy and partial myometrial resection (PMR) specimens.

PAS was determined by the presence of 1 or more placental cotyledons unable to be separated from the uterine wall at delivery or examination. Operating time, intraoperative estimated blood loss (EBL), and the number of packed red blood cell (PRBC) units transfused were reported.

One or more detailed transabdominal sonography (TAS) and TVS of the LUS, placenta, and pelvis were performed in patients within 2 weeks prior to delivery. Placenta measured with an edge of 0.5 cm to 2 cm was described as low lying, while placenta measured below 0.5 cm was described as placenta previa.

There were 111 pregnant patients included in the final analysis, 70 of which had 3 or more previous CDs. Seventy-six patients had abnormal placental tissue attachment at birth, with superficial villous attachment found in 11 and deep villous attachment in 65.

Hysterectomy was performed in 78% of patients with PAS and 37% with no evidence of PAS at birth. Nine percent of patients with conservative management had a focal area of abnormal placement confirmed as PAS on histology and managed through partial PMR and LUS. 

Patients with PAS had significantly higher median intraoperative EBL and the number of PRBC units transfused. Of cases, 21.6% were reported as low lying at the TAS and 9% at the TVS. The distribution of placental location significantly varied based on the examination method.

On TVS, 23.4% of cases were reported with thin LUSs, and 27.9% with very thin LUSs. Increased subplacental vascularity was reported in 42.3% of cases on TAS and cervical vascularity in 54.1% of cases on TVS. Lacuna score did not differ between examination methods.

Factors significantly associated with PAS at birth when found through TAS include increased subplacental vascularity and placental lacunae presence. PAS at birth was reported in all patients with both increased subplacental vascularity and bridging vessels, as well as those with a lacuna score of 3 or above.

Factors significantly associated with PAS at birth when found through TVS include intracervical lakes and the presence of placental lacuna. Of patients marked as high risk of PAS through TAS and TVS, 95% and 96% respectively presented with PAS at birth.

These results indicated efficacy of transvaginal ultrasound examination for predicting PAS risk. Investigators recommended transvaginal ultrasound examination of the lower uterine segment and cervix be included when evaluating patients at risk of complex cesarean delivery.

Reference

Jauniaux E, Hussein AM, Thabet MM, Elbarmelgy RM, Elmarbelgy RA, 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 Obstetrics & Gynecology. 2023;229(4):445.E1-445.E11. doi:10.1016/j.ajog.2023.05.004