rule of outlet

rule of out·let

an obstetric rule for determining whether the pelvic outlet will permit the passage of a fetus; the sum of the posterior sagittal diameter and the transverse diameter of the outlet must equal at least 15 cm if a normal sized baby is to pass.
Farlex Partner Medical Dictionary © Farlex 2012

rule of out·let

(rūl owt'lĕt)
An obstetric determination of whether the pelvic outlet will permit the passage of a fetus; the sum of the posterior sagittal diameter and the transverse diameter of the outlet must equal at least 15 cm if a normal-sized baby is to pass.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012