constriction ring, in normal labor a ridge on the inner uterine surface forms between the passively thinning lower uterine segment and the actively thickening upper uterine segment (corpus). In cases of premature rupture of membranes and/or prolonged or protracted labor, a thicker, more prominent pathological structure forms, termed a pathological retraction ring (of Bandl) or a pathological construction ring. This may also occur between the births of twins. If labor is impeded, cesarean birth may be required. Compare pathological retraction ring.
