Most impoant diameter of pelvis during labour is :

Ans. is a i.e. Interspinous diameter of the outlet Interspinous diameter is the distance between the two ischial spines and is the smallest diameter of the pelvis 10 cms. It corresponds to the transverse diameter nf mid pelvis (i.e. plane of least pelvis dimensions). Plane of least pelvis dimensions is of paicular impoance in labour as : Internal rotation occurs at this level.deg It marks the beginning of the forward curve of the pelvic axis.deg Most cases of deep transverse arrest occur here.deg Ischia' spines represent zero station of the head.deg External os is at this level.deg Besides these : It corresponds to origin of levator ani muscledeg and is a landmark used for pudendal blockdeg. Also know : Another impoant diameter of pelvis is the Posterior Sagittal diameter of the outlet as the prognosis for vaginal delivery in case of narrowing of midpelvis or pelvic outlet depends on it.