The smallest diameter of the true pelvis is:

Ans. is a, i.e. Interspinous diameterRef. Williams Obs. 24/e, p 32-33Friends, we have mugged up pelvis in detail for our undergraduate exams but for PGME exams you need not mug up each and everything about pelvis. All you need to know are some of the important diameters, which I am listing below.Diameters of PelvisDiameterInletMidpelvisOutletAnteroposteriorObstetric conjugate -10-10.5 cm11-11.5 cm11.5-13.5 cm True conjugate -11 cmDiagonal conjugate -12 cm Oblique12 cm Transverse13Interspinous diameter 10 cmIntertuberus diameter 11 cmPosterior sagittal diameter of outlet: It is an important diameter in case of obstructed labour caused by narrowing of the midpelvis or pelvic out let as the prognosis for vaginal delivery depends on the length of posterior sagittal diameter. Posterior sagittal diameter extends from tip of coccyx to a right angle intersection with a line between the ischial tuberosities. It usually exceed 7.5 cm.IOC for detecting CPD or pelvic assessment or adequacy is - MRI.Best method of detecting CPD-Trial of labor > MRI > manual pelvic assessment.Remember:Longest diameter of pelvis - Transverse diameter of inlet and anteroposterior diameter of anatomic outlet Q.Shortest major diameter of pelvis - Interspinous diameterLongest AP diameter of inlet - Diagonal conjugate QShortest AP diameter of inlet - Obstetric conjugate QOnly AP diameter measured clinically - Diagonal conjugate QCrtical obstetric conjugate - 10 cm (i.e. if obstetric conjugate is less than 10 cm vaginal delivery is not possible)