Placenta previa. Coloured pelvic magnetic resonance imaging (MRI) scan of a 36-year-old pregnant woman with placenta previa. This disorder involves the placenta (lower centre) covering the cervix, the exit to the uterus. The patient, who was unaware of the pregnancy, had failed to have a period for 33 weeks, and had instead been suffering irregular uterine bleeding due to this condition. The foetus (head down) is seen in sagittal view, revealing its brain (lower left).