Clinical Review

Diagnosing placenta accreta spectrum with prenatal ultrasound

OBG Manag. 2018 October;30(10):34-36, 38-44

References

Irving FC, Hertig AT. A study of placenta accreta. Surg Gynec Obstet. 1937:64:178–200.
Wu S, Kocherginsky M, Hibbard JU. Abnormal placentation: twenty-year analysis. Am J Obstet Gynecol. 2005;192:1458–1461.
Hall T, Wax JR, Lucas FL, et al. Prenatal sonographic diagnosis of placenta accreta—impact on maternal and neonatal outcomes. J Clin Ultrasound. 2014;42:449–455.
Bowman ZS, Eller AG, Kennedy AM, et al. Interobserver variability of sonography for prediction of placenta accreta. J Ultrasound Med. 2014;33:2153–2158.
Silver RM. Abnormal placentation: placenta previa, vasa previa, and placenta accreta. Obstet Gynecol. 2015;126:654–668.
Silver RM, Landon MB, Rouse DJ, et al; National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol. 2006;107:1226–1232.
Rac MW, Moschos E, Wells CE, et al. Sonographic findings of morbidly adherent placenta in the first trimester. J Ultrasound Med. 2016;35:263–269.
Ballas J, Pretorius D, Hull AD, et al. Identifying sonographic markers for placenta accreta in the first trimester. J Ultrasound Med. 2012;31:1835–1841.
Comstock CH, Bronsteen RA. The antenatal diagnosis of placenta accreta. BJOG. 2014;121:171–181.
Marshall NE, Fu R, Guise JM. Impact of multiple cesarean deliveries on maternal morbidity: a systematic review. Am J Obstet Gynecol. 2011;205:262.e1–e8.
Baughman WC, Corteville JE, Shah RR. Placenta accreta: spectrum of US and MR imaging findings. Radiographics. 2008;28:1905–1916.
Finberg HJ, Williams JW. Placenta accreta: prospective sonographic diagnosis in patients with placenta previa and prior cesarean section. J Ultrasound Med. 1992;11:333–343.
D’Antonio F, Iacovella C, Bhide A. Prenatal identification of invasive placentation using ultrasound: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2013;42:509–517.
Comstock CH, Love JJ Jr, Bronsteen RA, et al. Sonographic detection of placenta accreta in the second and third trimesters of pregnancy. Am J Obstet Gynecol. 2004;190:1135–1140.
D’Antonio F, Palacios-Jaraquemada J, Lim PS, et al. Counseling in fetal medicine: evidence-based answers to clinical questions on morbidly adherent placenta. Ultrasound Obstet Gynecol. 2016;47:290–301.
Hudon L, Belfort MA, Broome DR. Diagnosis and management of placenta percreta: a review. Obstet Gynecol Surv. 1998;53:509–517.
Wong HS, Cheung YK, Zuccollo J, et al. Evaluation of sonographic diagnostic criteria for placenta accreta. J Clin Ultrasound. 2008;36:551–559.
Jauniaux E, Collins S, Burton GJ. Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging. Am J Obstet Gynecol. 2018;218:75–87.
Rac MW, Dashe JS, Wells CE, et al. Ultrasound predictors of placental invasion: the Placenta Accreta Index. Am J Obstet Gynecol. 2015;212:343.e1–e7.
Pilloni E, Alemanno MG, Gaglioti P, et al. Accuracy of ultrasound in antenatal diagnosis of placental attachment disorders. Ultrasound Obstet Gynecol. 2016;47:302–307.
Comstock CH. Antenatal diagnosis of placenta accreta: a review. Ultrasound Obstet Gynecol. 2005;26:89–96.
Collins SL, Stevenson GN, Al-Khan A, et al. Three-dimensional power Doppler ultrasonography for diagnosing abnormally invasive placenta and quantifying the risk. Obstet Gynecol. 2015;126:645–653.
Collins SL, Ashcroft A, Braun T, et al; European Working Group on Abnormally Invasive Placenta (EW-AIP). Proposal for standardized ultrasound descriptors of abnormally invasive placenta (AIP). Ultrasound Obstet Gynecol. 2016;47:271–275.
Gilboa Y, Spira M, Mazaki-Tovi S, et al. A novel sonographic scoring system for antenatal risk assessment of obstetric complications in suspected morbidly adherent placenta. J Ultrasound Med. 2015;34:561–567.
Tovbin J, Melcer Y, Shor S, et al. Prediction of morbidly adherent placenta using a scoring system. Ultrasound Obstet Gynecol. 2016;48:504–510.
Jauniaux E, Collins SL, Jurkovic D, Burton GJ. Accreta placentation: a systematic review of prenatal ultrasound imaging and grading of villous invasiveness. Am J Obstet Gynecol. 2016:215:712–721.
Familiari A, Liberati M, Lim P, et al. Diagnostic accuracy of magnetic resonance imaging in detecting the severity of abnormal invasive placenta: a systematic review and meta-analysis. Acta Obstet Gynecol Scand. 2018;97:507–520.
Rezk MA, Shawky M. Grey-scale and colour Doppler ultrasound versus magnetic resonance imaging for the prenatal diagnosis of placenta accreta. J Matern Fetal Neonatal Med. 2016;29:218–223.
Expert Panel on MR Safety; Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document on MR safe practices: 2013. J Magn Reson Imaging. 2013;37:501–530.
Pekar-Zlotin M, Melcer Y, Maymon R, Jauniaux E. Secondtrimester levels of fetoplacental hormones among women with placenta accreta spectrum disorders. Int J Gynaecol Obstet. 2018;140:377–378.
Lyell DJ, Faucett AM, Baer RJ, et al. Maternal serum markers, characteristics and morbidly adherent placenta in women with previa. J Perinatol. 2015;35:570–574.

Other US markers of PAS

Retroplacental–myometrial interface

Loss of the normal hypoechoic (clear) retroplacental zone, also referred to as loss of the clear space between placenta and uterus, is another marker of PAS (FIGURE 5). This finding corresponds to pathologic loss of the decidua basalis as trophoblastic tissue invades directly through the myometrium.¹⁵ This sonographic finding has been reported to have a detection rate of approximately 93%, with sensitivity of 52% and specificity of 57%, for PAS; the false-positive rate, however, has been in the range of 21% or higher. This marker should not be used alone because it is angle-dependent and can be found (as an absent clear zone) in normal anterior placentas.¹⁶

The strength of this US marker is in its negative predictive value, which ranges from 96% to 100%. The presence of a hypoechoic retroplacental clear space that extends the length of the placenta makes PAS unlikely.¹⁷ Of note, the clear zone may appear falsely absent as a result of increased pressure from the US probe.

Retroplacental myometrial thickness

Another US finding characteristic of PAS is a retroplacental myometrial thickness of <1 mm (FIGURE 6).¹⁵ This finding can result from trophoblastic invasion with minimal intervening myometrium. A thin myometrium also may be due to partial dehiscence (the so-called uterine window) of the uterine wall.¹⁸

Retroplacental myometrial thickness is difficult to assess because the lower uterine-segment myometrium thins in normal pregnancy as term approaches. This measurement also can be influenced by direct pressure of the US probe and fullness of the maternal bladder.¹⁸ In patients who have had a CD but who do not have PAS, the median myometrial thickness of the lower uterine segment in the third trimester is 2.4 mm.¹⁹

ON OUR US UNIT……we optimize transabdominal US imaging of the retroplacental–myometrial interface by applying minimal transducer pressure on the abdomen, minimizing image depth, and magnifying image display. We use linear sweeps to image the entire placenta.

Thinning of the myometrium in the upper uterine segment always should be of concern. Studies of this marker have reported sensitivity of US ranging from 22% to 100% and specificity from 72% to 100%.^9,20 Given such variability, it is important to standardize the gestational age and sonographic approach for this marker.

AT OUR INSTITUTION……we typically approach retroplacental myometrial thickness transabdominally by applying minimal transducer pressure on the abdomen, minimizing image depth, and magnifying image display. We measure the myometrium at its thinnest point, taking the measurement perpendicular to the long axis of the wall of the uterus. In the presence of placenta previa or low-lying placenta, we take a transvaginal approach.

Continue to: Uterovesical interface

References

Irving FC, Hertig AT. A study of placenta accreta. Surg Gynec Obstet. 1937:64:178–200.
Wu S, Kocherginsky M, Hibbard JU. Abnormal placentation: twenty-year analysis. Am J Obstet Gynecol. 2005;192:1458–1461.
Hall T, Wax JR, Lucas FL, et al. Prenatal sonographic diagnosis of placenta accreta—impact on maternal and neonatal outcomes. J Clin Ultrasound. 2014;42:449–455.
Bowman ZS, Eller AG, Kennedy AM, et al. Interobserver variability of sonography for prediction of placenta accreta. J Ultrasound Med. 2014;33:2153–2158.
Silver RM. Abnormal placentation: placenta previa, vasa previa, and placenta accreta. Obstet Gynecol. 2015;126:654–668.
Silver RM, Landon MB, Rouse DJ, et al; National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol. 2006;107:1226–1232.
Rac MW, Moschos E, Wells CE, et al. Sonographic findings of morbidly adherent placenta in the first trimester. J Ultrasound Med. 2016;35:263–269.
Ballas J, Pretorius D, Hull AD, et al. Identifying sonographic markers for placenta accreta in the first trimester. J Ultrasound Med. 2012;31:1835–1841.
Comstock CH, Bronsteen RA. The antenatal diagnosis of placenta accreta. BJOG. 2014;121:171–181.
Marshall NE, Fu R, Guise JM. Impact of multiple cesarean deliveries on maternal morbidity: a systematic review. Am J Obstet Gynecol. 2011;205:262.e1–e8.
Baughman WC, Corteville JE, Shah RR. Placenta accreta: spectrum of US and MR imaging findings. Radiographics. 2008;28:1905–1916.
Finberg HJ, Williams JW. Placenta accreta: prospective sonographic diagnosis in patients with placenta previa and prior cesarean section. J Ultrasound Med. 1992;11:333–343.
D’Antonio F, Iacovella C, Bhide A. Prenatal identification of invasive placentation using ultrasound: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2013;42:509–517.
Comstock CH, Love JJ Jr, Bronsteen RA, et al. Sonographic detection of placenta accreta in the second and third trimesters of pregnancy. Am J Obstet Gynecol. 2004;190:1135–1140.
D’Antonio F, Palacios-Jaraquemada J, Lim PS, et al. Counseling in fetal medicine: evidence-based answers to clinical questions on morbidly adherent placenta. Ultrasound Obstet Gynecol. 2016;47:290–301.
Hudon L, Belfort MA, Broome DR. Diagnosis and management of placenta percreta: a review. Obstet Gynecol Surv. 1998;53:509–517.
Wong HS, Cheung YK, Zuccollo J, et al. Evaluation of sonographic diagnostic criteria for placenta accreta. J Clin Ultrasound. 2008;36:551–559.
Jauniaux E, Collins S, Burton GJ. Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging. Am J Obstet Gynecol. 2018;218:75–87.
Rac MW, Dashe JS, Wells CE, et al. Ultrasound predictors of placental invasion: the Placenta Accreta Index. Am J Obstet Gynecol. 2015;212:343.e1–e7.
Pilloni E, Alemanno MG, Gaglioti P, et al. Accuracy of ultrasound in antenatal diagnosis of placental attachment disorders. Ultrasound Obstet Gynecol. 2016;47:302–307.
Comstock CH. Antenatal diagnosis of placenta accreta: a review. Ultrasound Obstet Gynecol. 2005;26:89–96.
Collins SL, Stevenson GN, Al-Khan A, et al. Three-dimensional power Doppler ultrasonography for diagnosing abnormally invasive placenta and quantifying the risk. Obstet Gynecol. 2015;126:645–653.
Collins SL, Ashcroft A, Braun T, et al; European Working Group on Abnormally Invasive Placenta (EW-AIP). Proposal for standardized ultrasound descriptors of abnormally invasive placenta (AIP). Ultrasound Obstet Gynecol. 2016;47:271–275.
Gilboa Y, Spira M, Mazaki-Tovi S, et al. A novel sonographic scoring system for antenatal risk assessment of obstetric complications in suspected morbidly adherent placenta. J Ultrasound Med. 2015;34:561–567.
Tovbin J, Melcer Y, Shor S, et al. Prediction of morbidly adherent placenta using a scoring system. Ultrasound Obstet Gynecol. 2016;48:504–510.
Jauniaux E, Collins SL, Jurkovic D, Burton GJ. Accreta placentation: a systematic review of prenatal ultrasound imaging and grading of villous invasiveness. Am J Obstet Gynecol. 2016:215:712–721.
Familiari A, Liberati M, Lim P, et al. Diagnostic accuracy of magnetic resonance imaging in detecting the severity of abnormal invasive placenta: a systematic review and meta-analysis. Acta Obstet Gynecol Scand. 2018;97:507–520.
Rezk MA, Shawky M. Grey-scale and colour Doppler ultrasound versus magnetic resonance imaging for the prenatal diagnosis of placenta accreta. J Matern Fetal Neonatal Med. 2016;29:218–223.
Expert Panel on MR Safety; Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document on MR safe practices: 2013. J Magn Reson Imaging. 2013;37:501–530.
Pekar-Zlotin M, Melcer Y, Maymon R, Jauniaux E. Secondtrimester levels of fetoplacental hormones among women with placenta accreta spectrum disorders. Int J Gynaecol Obstet. 2018;140:377–378.
Lyell DJ, Faucett AM, Baer RJ, et al. Maternal serum markers, characteristics and morbidly adherent placenta in women with previa. J Perinatol. 2015;35:570–574.

Diagnosing placenta accreta spectrum with prenatal ultrasound

References

Other US markers of PAS

Retroplacental myometrial thickness

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