Impoance of the plane of midpelvis is

The pelvis is described as having four imaginary planes:The plane of the pelvic inlet--the superior strait. 2. The plane of the pelvic outlet--the inferior strait. 3. The plane of the midpelvis--the least pelvic dimensions. 4. The plane of greatest pelvic dimension--of no obstetrical significance.(Ref: William's Obstetrics; 25th edition)