This study aim to assess the accuracy of magnetic resonance imaging (MRI) compared to gray-scale and colour Doppler ultrasound (US) for the prenatal diagnosis of placenta accreta.

Placenta accreta occurs when the chorionic villi abnormally invade the myometrium. Based on histopathology it is divided into three grades: placenta accreta (the chorionic villi are in contact with the myometrium), placenta increta (the chorionic villi invade the myometrium), and placenta percreta where the chorionic villi penetrate the uterine serosa. With increasing rate of cesarean delivery, the incidence of both placenta praevia and placenta accreta is steadily increasing in frequency.

Prenatal diagnosis of invasive placentation is associated with a reduced risk of maternal complications as it allows a preplanned treatment of the condition . Gray-scale and colour Doppler ultrasound (US) are valuable tools in the prenatal diagnosis of placenta accreta .However, if the ultrasound ( US ) findings suggest possible percreta or are inconclusive or negative in an at-risk woman, magnetic resonance imaging (MRI) can be useful.

Multiple sonographic findings are seen with placenta accreta such as decrease in myometrial thickness, placenta previa, placental lacunae, abnormal pattern of color Doppler, loss of the retroplacental clear zone and placenta percreta irregularities in wall of urinary bladder ( UB ) have been detected .

The most magnetic resonance imaging characteristic findings seen in placenta accreta are nodular thickening in the dark zone of placenta-uterine interface together with extensions of dark bands through the placenta, outer uterine bulge causing from the mass effect of the placenta and heterogeneous signal intensity of placenta on the T2-weighted HASTE sequences due to large placental lakes and vessels.

Inclusion Criteria:

• Haemodynamically stable pregnant women who have the following risk factors for placenta accreta : persistent anterior placenta previa, prior uterine surgery (such as a previous cesarean section, uterine curettage, or myomectomy).
• Maternal age : 20-40 years old.
• BMI : 18-29.9 kg/m2.

Exclusion Criteria:

• Exclusion criteria will be MRI contraindications, cardiac pacemaker, metal objects in the body, and patient's refusal for MRI evaluation.
• Haemodynamically unstable patients.

Haemodynamically stable pregnant women, who attend the antenatal care clinic at Ain Shams University Hospital or are referred from other hospitals for further evaluation. The recruited patients have to fulfill the inclusion criteria,