Labour is defined as regular contractions bringing about progressive cervical changes. This is not linked to rupture of membranes (PPROM) or loss of the cervical 'show'.
Stages of Labour
- STAGE 1 – dilatation of cervix.
- Latent phase: Onset of labour to 4 cm dilation. In this time, the cervix becomes effaced i.e. shortened.
- Active Phase: Begins when cervix is 4 cm dilated. This is known as ‘active labour’. The actual onset of labour is defined as the ‘progressive dilatation’. The cervix dilates up to 10 cm; it is then ‘fully dilated’ and now wide enough for the baby’s head to pass through. This can take up to 20hrs in first time mothers. The most painful stage is >8 cm. The rate of cervical dilatation should be >0.5 cm an hour in the first pregnancy. The dilatation of the cervix is accompanied by effacement (thinning) of the cervix.
- STAGE 2 – expulsion
The cervix is fully dilated to the delivery of the fetus.
- Passive phase: Full dilation to onset of involuntary expulsive contractions
- Active phase: head is low in pelvis, so urge to push is present. This lasts less than 2 hours.
- STAGE 3 – placenta delivery (< 30 minutes, usually in a few minutes)
Mechanism of Delivery
- Engagement – foetal head engages with the pelvis in the transverse position
- Descent and flexion – the head descends down the birth canal and the neck flexes
- Internal rotation – the fetal head rotates 90° so that the baby’s head faces the mothers rectum
- Delivery by extension – the fetal head passes out of the birth canal. Its head is tilted forwards so that the crown of the head moves through the vagina first.
- Restitution - fetal head turns 45° to restore its normal position to the shoulders, which are still rotated
- External rotation – the shoulders repeat the movements of the head to align the whole body.
Increased oxytocin levels causes uterine muscle contractions, and prostaglandins soften the cervix. Progesterone levels decrease at the end of pregnancy.
It is important to establish the rhesus status of the mother (after labour, ectopics or miscarriages) as maternal and fetal blood gets mixed during labour. This is important because if the mother is rhesus negative, and the fetus is rhesus positive, a maternal immunological response is established against
rhesus positive blood. This will not affect the current pregnancy (as the mixing only occurs during labour, miscarriage or termination), however it will affect subsequent pregnancies leading to hypoxic, ‘blue’ babies and even miscarriage. To prevent the establishment of the immunological response Anti D is given, which stops the production of maternal antibodies against rhesus positive blood. A Kleihaur test can be performed to see how much maternal and fetal blood has mixed, to determine whether Anti D is needed.
- Check maternal rhesus status following labour, Miscarriage or termination
- If rhesus negative give Anti D
This should be done for each pregnancy.