Page created on November 22, 2021. Not updated since.
Labour (childbirth) is the last phase of pregnancy, which ends with the foetus, placenta, and foetal membranes being expulsed through the vaginal canal or by Caesarean section. In most cases they begin spontaneously, but in some cases, labour must be induced (topic B23). Although it’s sometimes called childbirth, labour doesn’t end when the foetus is out of the birth canal; there are two more stages after this.
Normal labour (partus normalis) refers to childbirth without complications, occurring in weeks 37 – 42 in normal presentation (cephalic), induced or spontaneous. Labour takes longer in nullipara (not had labour before) than in multipara (had labour before).
There are four stages of labour (although many don’t consider the fourth stage its own stage and instead refer to three stages). During labour, the water “breaks” due to the amniotic membrane rupturing. The water may “break” during the first or second stage, but most commonly in the first stage.
First stage – stage of dilatation
Introduction and onset
The first stage of labour is the stage of dilatation. During this stage the cervix dilates from being closed to being open with an opening of 10 cm in diameter. This is necessary for the foetus to pass. It lasts 12 – 14 hours in nullipara and 6 – 8 hours in multipara.
This stage begins with the onset of true labour pain and regular contractions. “True labour pain” is strong pain related to contractions which last 30 – 70 seconds and come about 5 – 10 minutes apart. Pain is felt in the abdomen and lower back. These contractions then increase in frequency, duration, and intensity.
We can divide this stage into two phases: the latent phase and the active phase. The latent phase takes 4 – 8 hours. During this phase, the first 3 cm of cervical dilatation occur.
The active phase takes less time as the contractions become more effective and the cervix dilates more quickly. During the phase, the cervix dilates the remaining 7 cm.
The stage of dilatation ends when the cervix is fully dilated and the presenting part of the foetus is in the pelvic inlet. This it the most common time for membrane rupture.
During the first stage, it’s important to periodically assess the uterine contractions and the cervical dilation, as well as provide sufficient analgesia (topic B11).
Second stage – stage of pushing and foetal expulsion
Introduction and onset
The second stage of labour is the stage of pushing and foetal expulsion. It begins after the first stage (when the cervix is fully dilated and the presenting part of the foetus is in the pelvic inlet). It lasts approximately 1 hour in nulliparous and 30 min in multipara.
During this stage, the mother should push during each contraction (and rest between them). With each push and each contraction, the foetus gets further and further down in the birth canal and closer and closer to expulsion, until eventually it has been completely expulsed from the birth canal.
As the foetal head is so large compared to the pelvis, the foetus must undergo several movements and rotations during this stage to fit through the birth canal. This allows the foetus to adjust to the dimensions of the pelvis. The narrowest diameter of the pelvis is the anterio-posterior (AP) diameter, at 9,5 – 12,5 cm.
First, as the head descends into the pelvis the foetus faces the mother’s left or right, and eventually becomes engaged (meaning the widest part of the foetal head, the biparietal diameter, has passed the pelvic inlet). Then, the foetal head descends further. As it’s pushed further down, the neck is flexed. At this time, the head is flexed and the foetus is facing the mother’s left or right.
Then, foetus rotates internally so that it faces the mothers back again. The head is birthed in this position while the neck extends, causing the back of the head to be birthed first. Then, the foetus rotates externally again, back to facing left or right (while the head is out but not the rest). Downward traction is applied to the head so that the anterior shoulder is birthed first. Then, upward traction is applied, so that the posterior shoulder is birthed. Afterward, the rest of the foetus is expulsed easily.
In summary, the order of events are the following: Engagement, descent, flexion -> Internal rotation -> Extension and expulsion of the head -> External rotation -> Expulsion of the body
This stage ends when the foetus has been completely expulsed.
During the second stage, it’s important to periodically assess the uterine contractions with continuous CTG. Oxytocin can be used to stimulate contractions if they’re insufficient. If the foetus is stuck in the vaginal opening, episiotomy can be performed to prevent rupture of the perineum (which may affect the anal sphincter). Otherwise, operative delivery may be needed (topic A5).
Third stage – placental stage
Introduction and onset
After the foetus has left the birth canal, the placenta and foetal membranes must be “birthed” as well. This may occur anywhere from immediately after stage 2 to 10 – 30 minutes after.
As the placenta separates from the uterine wall, it may separate in two ways. The most common is when separation begins in the centre of the placenta (Schultz method). This causes a clot to form, which causes the least amount of bleeding. However, in 30% of cases, separation begins at the edge of the placenta (Duncan method). In this case, no clot can form, and so bleeding is more severe.
Once separation has occurred, the uterine wall contracts strongly. This forces the placenta and foetal membranes out, as well as compressing bleeding uterine vessels.
This stage ends when the placenta and foetal membranes are out.
During this stage we give routinely oxytocin to help the contraction and to reduce postpartum bleeding risk.
Fourth stage – post-placental stage
The fourth stage involves close monitoring for the first 2 hours, visual exploration for any injuries, and suturing if necessary.
The placenta and foetal membranes must be examined whether they’re whole or not, as any remnants left inside the uterine cavity will get infected and must be removed.
Any bleeding must be stopped. If bleeding occurs, tranexamic acid, oxytocin, and massaging the uterus may be used to stop it.