Radiology General 13c3b382 Frequency for trans vaginal USG for obstetric purpose A 3 - 5 MHz B 5 -7.5 MHz C 7.5 - 20 MHz D > 20 MHz High-Yield Explanation Transabdominal USG - 3 - 5 MHz. Trans vaginal USG - 5 - 7.5 MHz.