Shoulder Dystocia
Shoulder dystocia is impaction of a fetal shoulder against the maternal pelvis after the head has delivered, so the shoulders will not follow routine axial traction.
Definition
A vaginal cephalic delivery that requires additional obstetric manoeuvres to deliver the fetus after the head has delivered and gentle traction has failed. An objective diagnosis of a head-to-body delivery time longer than 60 seconds has also been proposed, but these data are not routinely collected. The anterior shoulder impacts on the maternal symphysis, or less commonly the posterior shoulder on the sacral promontory.
First principles
The diagnosis is a failed pull, not a sign
The definition is behavioural, not anatomical: it is the birth that needed extra manoeuvres after the head came out and gentle traction failed. That matters because you cannot see the impaction. Classically the head retracts tightly against the perineum, the so-called turtle sign, but the RCOG definition rests on the failed traction, not on any sign. Impaction is usually of the anterior shoulder behind the pubic symphysis, which is why the first manoeuvres are aimed at that shoulder. So the bedside question is not what you can see, it is whether the shoulders followed.
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