During normal birth, what is known as a ‘retraction ring’ forms in the uterus. This is a ridge that forms between the upper and lower part of the uterus as a result of contractions. Usually, when a muscle contracts, what happens is that the muscle fibres get shorter while it’s contracting, and then go back to their normal length afterwards. When the uterus contracts in labour, though, the muscle fibres retract, which means that they hold part of the contraction and don’t go back to their normal length afterwards, so that they become progressively shorter with each contraction. In labour, it’s mainly the upper part (segment) of the uterus that contracts and retracts. This pulls on the bottom part (the lower segment), especially on the area of the cervix, causing it to thin out. (Incidentally, if you have a caesarean, it’s the lower segment that is opened to perform the operation, hence the initials LSCS – for lower segment caesarean section.) The retraction ring is the ridge that gradually forms between the shortened, thickened muscles of the upper segment of the uterus, and the thin, stretched lower segment. A Bandl’s ring is an exaggerated pathological form of this retraction ring. It forms when, for some reason or another, labour becomes obstructed. This may happen when there is cephalopelvic disproportion (the baby won’t fit through the pelvis), or it may be associated with the baby being in an unfavourable position. The ring actually becomes visible through the abdomen above the symphysis pubis (the pubic joint), and, as you rightly, say means the baby can’t be pushed out vaginally. If left untreated, the uterus would eventually rupture. This is why a caesarean is performed.