A 32-year-old G3P2 with two prior caesarean sections undergoes ultrasound at 20 weeks. The placenta is anterior, low-lying, and loss of the retroplacental clear zone is noted on Doppler. The most likely diagnosis and the investigation of choice to confirm placental invasion depth are:
- A Placenta accreta spectrum; MRI pelvis ✓
- B Placenta praevia; repeat ultrasound at 32 weeks
- C Vasa praevia; transvaginal colour Doppler
- D Abruptio placentae; Kleihauer-Betke test
Correct answer: A. Placenta accreta spectrum; MRI pelvis
Explanation
Loss of the retroplacental hypoechoic zone and lacunae on ultrasound in a patient with prior uterine surgery and anterior placenta strongly suggests placenta accreta spectrum (PAS). MRI is the investigation of choice when ultrasound is equivocal for assessing the depth of invasion (accreta vs increta vs percreta) and involvement of adjacent structures. Vasa praevia is a different entity involving fetal vessels overlying the internal os.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.