Placenta Accreta : Contrast-enhanced Ultrasound Analysis in High Risk Population

Abnormally invasive placenta (AIP) is defined as an abnormal placental attachment of a part or the entire chorionic plate with penetration of chorionic villi in the myometrium and absence of the decidua basalis. This anomaly is associated with significant maternal morbidity and mortality as it may result in severe haemorrhage during the post-partum. It has been demonstrated that prenatal diagnosis of AIP is essential to reduce maternal morbidity. In a recent study of Chantraine F. et al. prenatal diagnosis of AIP leads to better outcomes, due to fewer emergency operations and less mass transfusions. Currently, the diagnosis of AIP is based on a combination of conventional B-mode ultrasound and MRI. However, prenatal diagnosis of AIP remains challenging and recent reports demonstrated it is achieved in only thirds of cases.

Contrast enhanced ultrasound (CEUS) is a non-invasive technique based on the detection by ultrasound (US) of gas-filled microbubbles used as perfusion tracers. Intravascular rheological properties of these bubbles are similar to those of red blood cells and they remain entirely within the intravascular space. Previous studies have demonstrated that microbubbles do not transfer into fetal circulation. CEUS has been used for years in many US imaging applications (e.g. liver, kidneys and breast). In obstetrics, despite not yet approved for clinical use, CEUS offers the opportunity to analyze anatomical placental landmarks, improving the contrast between placenta and myometrium. In addition, quantification parameters related to the contrast enhancement have been proposed as objective indicators to estimate blood perfusion rates in the placental intervillous space.

The main objective of this study is to provide pre-clinical evaluation of CEUS for the diagnosis of AIP and to try to determine if AIP are characterised by differences in intervillous blood rheological properties. Conventional CEUS parameters will be: rise time, peak enhancement, wash-in rate, mean transit time and wash-in area under the curve.

As this study is a pre-clinical evaluation, sample size calculation remains subjective and imprecise. For this reason, a sample size of 100 pregnant women to be included in this prospective study has been decided.

The potential impact of this study will be to propose a more reliable tool with both improved sensibility and specificity compared to the combination US/MRI and therefore to reduce the maternal worldwide burden of AIP.