Second stage of labour: definition and processes
The second stage of labour begins at full dilatation (the cervix, or neck of the womb, fully open at about 10 cm) and ends with the birth of the baby.
Remember
In the second stage the baby's descent and the rotation of its head are passive, and the mother's pushing is the active part that adds to the force of the womb's contractions.
Memory aid
stage 1 opens the door, stage 2 sends the baby through and stage 3 delivers the placenta
Picture a door: the first stage opens it, the second stage sends the baby through it and the third stage delivers the placenta.
Labour has three stages, and the second is defined by its start and end points. In the first stage the cervix softens, shortens, thins and opens until it is fully dilated. The second stage begins once the cervix is fully open, at about 10 cm, and ends with the birth of the baby. The third stage then runs from the birth to delivery of the placenta and membranes (the afterbirth).
When the cervix is fully open, the contractions of the womb change character. They become expulsive, which means they push the baby down the birth canal (the passage through the pelvis and vagina) instead of opening the cervix.
Two kinds of process work together in this stage. The passive ones belong to the baby: it descends, and its head rotates and flexes (the chin moves towards the chest), so the head meets less resistance. The active one is the mother's voluntary pushing, which adds to the force of the contractions. The two overlap, because a woman can push during contractions whenever she feels the urge. The second stage also includes a passive phase before the mother's active pushing begins, so its start is judged by full dilatation rather than by the urge to push.
The head moves in a set order. It flexes and rotates first, then crowns (stretches the perineum, the skin and muscle between the vagina and anus), extends, and undergoes restitution (turning back to line up with the shoulders). The shoulders and then the rest of the body are delivered.
Key facts
- Starts
- at full dilatation, when the cervix is open to about 10 cm
- Ends
- with the birth of the baby, not delivery of the placenta
- Passive elements
- descent of the baby, and rotation and flexion of its head, which lessen what the head presents to the birth canal
- Active element
- the mother's pushing, which adds to the expulsive contractions
- Neighbouring stages
- the first stage ends at full dilatation, and the third stage runs from the birth to delivery of the placenta and membranes
- Order of head movements
- flexion and internal rotation come before crowning and extension
Exam traps
- Pushing does not complete the opening of the cervix, because shortening, thinning and opening of the cervix belong to the first stage, and the second stage begins only once the cervix is fully dilated.
- Extension of the head does not come first, because the flexed head is the one that presents less to the birth canal, and extension comes later, once the head has crowned.
- Contractions of the womb do not stop at full dilatation, because they become expulsive and the mother can push during them, so the two forces work together.
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