Prospective First‐Trimester Ultrasound Imaging of Low Implantation and Placenta Accreta Spectrum

Abstract

Objectives-To prospectively evaluate low implantation of the gestational sac and other first-trimester ultrasound (US) parameters for prediction of placenta accreta spectrum (PAS). Methods-Women with a diagnosis of low implantation on clinically indicated first-trimester US underwent a transvaginal US examination at 10 to 13 weeks' gestation to assess the trophoblast location, anechoic areas, bridging vessels, and smallest myometrial thickness (SMT). The placental location was evaluated in the second trimester, and serial US examinations were performed in cases of low placentation. Placenta accreta spectrum was based on clinical findings and confirmed by histologic results. Results-Of 68 women, 40 (59%) had prior cesarean delivery (CD). Hysterectomy was performed in 8, all with prior CD. Of these, 7 (88%) had US suspicion of PAS. In 16 with prior CD and basalis overlying the internal os, 9 (56%) had second-trimester placenta previa, and 7 of 9 (78%) underwent hysterectomy with pathologic confirmation of PAS. Of 28 without prior CD, there were no cases of persistent low placentation in the third trimester regardless of the trophoblast location. Ultrasound parameters associated with PAS were a smaller distance from the inferior trophoblastic border to the external os, disruption of the bladder-serosal interface, bridging vessels, anechoic areas, and the SMT. In women with prior CD, use of the SMT in the sagittal plane yielded an area under the receiver operating characteristic curve of 0.96 (95% confidence interval, 0.91-1.00). Conclusions-First-trimester low implantation increases the risk of persistent placenta previa and PAS in women with prior CD. All parameters were associated with PAS, the most predictive being the SMT. Key Words-cesarean scar pregnancy; first-trimester ultrasound; low implantation; placenta accreta spectrum P lacenta accreta spectrum (PAS) is a life-threatening obstetric complication occurring when the placenta abnormally adheres to or invades the myometrium. Once rare, PAS now complicates as many as 1 per 300 pregnancies in the United States, with the substantial rise in the incidence paralleling the rise in cesarean delivery (CD) rates, a known risk factor for PAS. 1-3 When compared with intrapartum diagnosis, prenatal diagnosis of PAS improves maternal outcomes by allowing for multidisciplinary planning and delivery before the onset of labor, vaginal bleeding, or both, thus reducing maternal and fetal morbidity. 2,4-7

Predicting Placenta Accreta Spectrum

“…Based on retrospective and prospective series, it has become increasingly apparent that the smallest myometrial thickness of the trophoblastic implantation on the cesarean scar, sometimes referred to as the niche, now known as cesarean scar pregnancy, can be a predictor of development of PAS later in gestation. [28][29][30] Relatively recently, the diagnosis of invasion has been expanded to include both clinical and histologic diagnoses of PAS according to FIGO classifications. 23 We used the respective FIGO classifications, as noted in our results.…”

“…Finally, although outside the scope of this project, it is important to mention that much of the recent interest and attention has been placed on early diagnosis of PAS in the first trimester. Based on retrospective and prospective series, it has become increasingly apparent that the smallest myometrial thickness of the trophoblastic implantation on the cesarean scar, sometimes referred to as the niche, now known as cesarean scar pregnancy, can be a predictor of development of PAS later in gestation 28–30 …”

Transvaginal Color Mapping Ultrasound in the First Trimester Predicts Placenta Accreta Spectrum: A Retrospective Cohort Study

“…The prospective study took place between May 2013 and July 2017 and was a singlecenter study. 12 Women were included if they were diagnosed with low implantation on a clinically indicated first-trimester US and subsequently underwent a TV US study at 10 0/7 to 13 6/7 weeks' gestation. Inclusion criteria also were presence of an appropriate transverse TV cine clip.…”

“…Based on retrospective and prospective series, it has become increasingly apparent that although these implantations on the scar may implant into the scar, rupture does not occur, but rather the fetus grows within the endometrium, the placenta undergoes extensive trophotrophism, and PAS ensues in a subgroup. [10][11][12] Most recently, the term cesarean scar pregnancy has been employed to replace other nomenclature to describe this trophoblastic implantation on the uterine scar in the first trimester. [13][14][15] Furthermore, Kaelin Agten et al described the idea of a dehiscent cesarean scar, referred to as a "niche," and how those pregnancies have different outcomes compared to an intact cesarean scar.…”

“…16 Other first trimester findings that have been associated with PAS include reduced myometrial thickness between the gestational sac and the bladder, irregularity of the bladder-uterine serosal interface, and the presence of anechoic areas. [10][11][12][17][18][19][20][21][22][23][24][25][26] Power Doppler has also been employed in the first trimester and shows promise for evaluation of future development of both placental invasion and insufficiency. [27][28][29] Oftentimes, the subjectivity of the impression associated with several of these methods makes it difficult to be applied universally and we therefore sought to determine if a postprocessing program could do as well as the interpretation of an experienced sonologist.…”