Labour and delivery normally occur between 37 and 42 weeks gestation.
There are three stages of labour:
- The first stage is from the onset of labour (true contractions) until 10cm cervical dilatation.
- The second stage is from 10cm cervical dilatation to delivery of the baby.
- The third stage is from delivery of the baby to delivery of the placenta.
Prostaglandins act like local hormones, triggering specific effects in local tissues. Tissues throughout the entire body contain and respond to prostaglandins. They play a crucial role in menstruation and labour by stimulating contraction of the uterine muscles. They also have a role in the ripening of the cervix before delivery.
One key prostaglandin to be aware of is prostaglandin E2. Pessaries containing prostaglandin E2 (dinoprostone) can be used to induce labour.
Braxton-Hicks contractions are occasional irregular contractions of the uterus. They are usually felt during the second and third trimester. Women can experience temporary and irregular tightening or mild cramping in the abdomen. These are not true contractions, and they do not indicate the onset of labour. They do not progress or become regular. Staying hydrated and relaxing can help reduce Braxton-Hicks contractions.
The first stage of labour is from the onset of labour (true contractions) until the cervix is fully dilated to 10cm. It involves cervical dilation (opening up) and effacement (getting thinner from front to back). The “show” refers to the mucus plug in the cervix, that prevents bacteria from entering the uterus during pregnancy, falling out and creating space for the baby to pass through.
The first stage has three phases:
- Latent phase: From 0 to 3cm dilation of the cervix. This progresses at around 0.5cm per hour. There are irregular contractions.
- Active phase: From 3cm to 7cm dilation of the cervix. This progresses at around 1cm per hour, and there are regular contractions.
- Transition phase: From 7cm to 10cm dilation of the cervix. This progresses at around 1cm per hour, and there are strong and regular contractions.
The second stage of labour lasts from 10cm dilatation of the cervix to delivery of the baby. The success of the second stage depends on “the three Ps”: power, passenger and passage.
Power: the strength of the uterine contractions.
Passenger: the four descriptive qualities of the fetus:
- Size: particularly the size of the head as this is the largest part.
- Attitude: the posture of the fetus. For example, how the back is rounded and how the head and limbs are flexed.
- Lie: the position of the fetus in relation to the mother’s body:
- Longitudinal lie – the fetus is straight up and down.
- Transverse lie – the fetus is straight side to side.
- Oblique lie – the fetus is at an angle.
- Presentation: the part of the fetus closest to the cervix:
- Cephalic presentation – the head is first.
- Shoulder presentation – the shoulder is first.
- Breech presentation – the legs are first. This can be:
- Complete breech – with hips and knees flexed (like doing a cannonball jump into a pool)
- Frank breech – with hips flexed and knees extended, bottom first
- Footling breech – with a foot hanging through the cervix
Passage: the size and shape of the passageway, mainly the pelvis.
Cardinal Movements of Labour
There are seven cardinal movements of labour:
- Internal Rotation
- Restitution and external rotation
Obstetricians describe the position of the baby’s head in relation to the mother’s ischial spines during the descent phase. Descent is measured in centimetres, from:
- -5: when the baby is high up at around the pelvic inlet
- 0: when the head is at the ischial spines (this is when the head is “engaged”)
- +5: when the fetal head has descended further out
The third stage of labour is from the completed birth of the baby to the delivery of the placenta.
Physiological management is where the placenta is delivered by maternal effort without medications or cord traction.
Active management of the third stage is where the midwife or doctor assist in delivery of the placenta. Active management shortens the third stage and reduces the risk of bleeding. Haemorrhage, or more than a 60-minute delay in delivery of the placenta, should prompt active management. Active management can be associated with nausea and vomiting.
Active management involves giving a dose of intramuscular oxytocin to help the uterus contract and expel the placenta. Careful traction is applied to the umbilical cord to guide the placenta out of the uterus and vagina.
Last updated May 2020