First‐trimester ultrasound diagnostic features of placenta accreta spectrum in low‐implantation pregnancy

Low-implantation pregnancy (LIP) is an important marker for the diagnosis of placenta accreta spectrum (PAS) in the first trimester. Many grayscale and color Doppler ultrasound markers of PAS have been defined in the second and third trimesters of pregnancy, but have not been studied in the first trimester. The aim of this study was to determine whether PAS sonographic markers could be used in the first trimester to differentiate patients with LIP who develop PAS from those who do not.This was a retrospective case-control study of women who delivered at our institution between 2009 and 2019. Cases were women with PAS who delivered by Cesarean hysterectomy and who had undergone first-trimester ultrasound demonstrating LIP. Controls were women with persistent placenta previa without PAS who delivered by Cesarean section without postpartum hemorrhage and who had undergone first-trimester ultrasound demonstrating LIP. Sonographic images were reviewed by an investigator blinded to pregnancy outcome and ultrasound reports. Images were reviewed for presence of abnormal uteroplacental interface, increased lower uterine segment hypervascularity and placental lacunae, with or without swirling on grayscale or color Doppler ultrasound.Following review of the electronic health records, 21 cases and 46 controls met the inclusion criteria. Placental lacunae were present in 18/21 (85.7%) cases and 7/46 (15.2%) controls (odds ratio (OR), 33.4; 95% CI, 7.7-144.4; P < 0.001). The number of lacunae was significantly higher in cases compared with controls, with a median of five lacunae present in cases compared with a median of one lacuna in controls (P < 0.001). The median size of the lacunae was also significantly larger in cases compared with controls, measuring 10.03 (interquartile range (IQR), 7.3-12.05) mm and 4.15 (IQR, 4.05-5.05) mm, respectively (P = 0.001). Lacunae swirling on grayscale or color Doppler ultrasound was noted only in PAS cases, with 10/12 (83.3%) having swirling on grayscale ultrasound and 12/12 (100%) having swirling on color Doppler (P < 0.001). Presence of an abnormal uteroplacental interface was also observed only in PAS cases, at a rate of 17/20 (85.0%) (P < 0.001). Lower uterine segment (uterovesical, subplacental and/or intraplacental) hypervascularity was present in 14/14 (100%) cases and only 1/12 (8.3%) controls (P < 0.001).In women at risk of PAS, ultrasound markers of PAS can and should be assessed as early as in the first trimester. The use of a first-trimester prenatal ultrasound screening protocol and standardized approach to ultrasound examination in at-risk mothers may help increase detection of PAS and enable planning for optimal management of affected pregnancies. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.