Placental Separation Mechanisms and Signs
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Direct answer
Placental separation occurs by the Schultze or Matthews Duncan mechanism, after which the placenta is expelled as the uterus contracts. Schultze separation starts at the centre and delivers the shiny fetal surface first, while Duncan separation starts at the edge and delivers the ragged maternal surface first. Reliable signs of separation are a gush of blood, lengthening of the cord and a globular, firm uterus that rises in the abdomen.
What you must remember
- Schultze mechanism: separation begins at the centre, so the shiny fetal surface presents first; it is the commoner pattern, often quoted at about 80 per cent.
- Matthews Duncan mechanism: separation begins at the edge, so blood escapes along the margin and the ragged maternal surface presents first.
- Site of separation: the placenta separates through the spongy layer (decidua spongiosa) of the decidua basalis; Nitabuch's layer is the fibrinoid layer above it, which is deficient in accreta.
- Retroplacental haematoma: blood that collects behind the separating placenta as the spiral arteries are torn, which is physiological at delivery.
- Gush of blood: a sudden release of retroplacental blood, which is one sign of separation.
- Cord lengthening: the cord appears to descend further out of the vulva as the placenta moves down.
- Kustner's sign: suprapubic pressure pushes the uterus upward; if the cord is drawn back into the vagina the placenta has not separated, and if it stays put the placenta has separated.
Comparing the two mechanisms
Separation is a process rather than a single event, and the mechanism determines both the surface of the placenta that delivers first and the way blood escapes. Learn the two mechanisms as a pair, because the surface that presents identifies the mechanism at once.
| Feature | Schultze | Matthews Duncan |
|---|---|---|
| First site of separation | Centre of the placenta | Edge (margin) of the placenta |
| Surface presenting at introitus | Shiny fetal surface, covered by amnion | Ragged maternal surface |
| Path of blood loss | Collects behind the placenta, then exits with delivery | Escapes along the margin from the outset |
| Sequence of delivery | Placenta slides down with the fetal side leading | Edge lifts first, and the membranes may appear first |
| Frequency | Commoner, the majority of cases | Less common, a minority of cases |
Clinically, the mechanism rarely changes management, but it explains why blood may appear before the placenta is seen. The shiny-fetal and ragged-maternal distinction is the quickest test in viva questions.
Where the exam tries to catch you
Examiners often reverse the two mechanisms, so anchor each one to its presenting surface.
- Trap: reversing Schultze and Duncan Correct: Schultze delivers the shiny fetal surface first from the centre, while Duncan delivers the ragged maternal surface first from the edge.
- Trap: treating a gush of blood alone as proof of complete separation Correct: the gush is one sign, so confirm it with cord lengthening and a globular, firm uterus before applying traction.
- Trap: pulling the cord before separation is complete Correct: traction before separation risks cord avulsion and uterine inversion, so wait for the signs.
- Trap: calling the retroplacental blood at separation an abruption Correct: that blood is physiological, whereas abruption is pathological separation before delivery.
Frequently asked questions
What is the difference between the Schultze and Matthews Duncan mechanisms?
In the Schultze mechanism, the placenta separates from the centre and delivers its shiny fetal surface first, whereas in the Matthews Duncan mechanism it separates from the edge and delivers its ragged maternal surface first. Schultze is the commoner pattern.
Which sign confirms placental separation?
No single sign confirms placental separation, but a gush of blood, lengthening of the cord and a globular, firm uterus that rises in the abdomen together indicate that separation has occurred. Controlled cord traction is applied only once these signs are present.
What is Kustner's sign?
Kustner's sign is a test in which the hand presses above the symphysis pubis to push the uterus upward, and if the cord retracts back into the vagina, the placenta has not yet separated. It helps decide whether it is safe to proceed with controlled cord traction.
Where does placental separation take place?
Placental separation takes place through the spongy layer (decidua spongiosa) of the decidua basalis, not through Nitabuch's fibrinoid layer, which is deficient in accreta. Blood from torn spiral arteries collects between the placenta and the uterine wall as the separation proceeds.
Why is the retroplacental haematoma normal at delivery?
The retroplacental haematoma is normal at delivery because the spiral arteries are torn as the placenta separates, and the blood collects behind it until expulsion. This differs from an antepartum abruption, which is pathological separation of the placenta before birth.