- retraction ring
- a depression in the uterine wall marking the junction between the actively contracting muscle fibres of the upper segment of the uterus and the muscle fibres of the lower segment. This depression is not always visible and is normal. In obstructed labour (e.g. contracted pelvis or malposition of the fetus resulting in shoulder presentation), the muscle fibres of the upper segment become shorter and thicker; the muscle fibres of the lower segment, on the other hand, become elongated and thinner. The junction between the two becomes more distinct as it rises into the abdomen from the pelvis. This abnormal ring is known as Bandl's ring and is a sign of impending rupture of the lower segment of the uterus, which becomes progressively thinner as Bandl's ring rises upwards. Immediate action to relieve the obstruction is then necessary, usually in the form of Caesarean section.
The new mediacal dictionary. 2014.