Constriction Ring: Key Characteristics

A constriction ring (also called a localized ring of spasm) is a benign, localized band of myometrial spasm that can develop at any level of the uterus during labour, most often around a poorly descended fetal part (e.g., the neck in a face presentation, or below the umbilicus after manipulation). It must be distinguished from Bandl's ring (the pathological retraction ring), which is an entirely different entity forming strictly at the junction of the upper and lower uterine segments in obstructed labour and is a warning sign of impending uterine rupture. This question tests exactly that distinction.

Statement Evaluation

• Statement 1: Premature rupture of membranes is a high-risk factor — Correct. Constriction rings are classically precipitated by conditions that lead to loss of liquor and direct uterine wall-to-fetus contact/irritability, such as premature rupture of membranes, mismanaged third stage of labour, and injudicious/excessive use of oxytocic agents. These factors provoke localized myometrial spasm.
• Statement 2: It is situated at the junction of upper and lower uterine segment — Correct (in this classification). A constriction ring is described as being able to occur anywhere along the uterus, including at the junction of the upper and lower segments; unlike Bandl's ring, however, its location is variable rather than fixed. As per the standard teaching used for this question, this statement is accepted as true for constriction ring.
• Statement 3: Uterus never ruptures — Correct. A constriction ring is a benign, self-limiting spasm and is not associated with an increased risk of uterine rupture, in sharp contrast to Bandl's ring, which precedes rupture in obstructed labour. This is the key differentiating feature between the two entities.
• Statement 4: The ring is felt per abdomen — Incorrect. Because a constriction ring is a localized band of spasm low in the uterine cavity, it is appreciated only on per-vaginal examination as a tight, non-relaxing band around the fetal part; it is not palpable abdominally. (It is Bandl's ring — not the constriction ring — that rises progressively and becomes palpable per abdomen as a transverse ridge, signalling impending rupture.)

Why the Other Options Are Wrong

• 2, 3 and 4: Incorrectly includes statement 4 (not felt per abdomen) and omits statement 1, a well-recognised risk factor.
• 1, 2 and 4: Incorrectly includes statement 4 and omits statement 3 (uterus does not rupture with a constriction ring).
• 1, 3 and 4: Incorrectly includes statement 4 and omits statement 2.

Conclusion

The correct combination is statements 1, 2 and 3, corresponding to option "1, 2 and 3" — premature rupture of membranes is a risk factor, the ring can occur at the upper–lower segment junction, and the uterus does not rupture with a constriction ring, which (unlike Bandl's ring) is not palpable per abdomen.