POCS patient going through IUI process - had two sonograms with first IUI; both normal . Sonogram at 2nd IUI showed dark spots or shadows. 2nd IUI performed 17 days ago; pregnancy test negative, started period today. Called doctors office and was told an MRI would need to be performed next week and sonogram for 3rd IUI scheduled. What causes dark spots or shadows. Seem to have formed in last two months; not noted on 1st two sonograms