Labour Flashcards
Describe the stages of labour?
Painful contractions lead to dilatation of the cervix
First stage – from the onset of labour (true contractions) until 10cm cervical dilatation
Second stage – from 10cm cervical dilatation until delivery of the baby
Third stage – from delivery of the baby until delivery of the placenta
What are the three mechanical factors that determine progress during labour?
POWER - the degree of force expelling the foetus
PASSAGE - the dimensions of the pelvis and the resistance of soft tissue
PASSENGER - the diameters of the foetal head
How is power of labour established?
Once labour established, the uterus contracts for 45-60 seconds every 2-4 minutes.
This pulls the cervix up (effacement) and causes dilation.
Aided by the pressure of the head as the uterus pushes the head down into the pelvis
Poor uterine activity is a common feature of the nulliparous women and induced labour. Rare in multiparous women
What are the three principle planes of the bony pelvis?
Inlet - 13cm transverse diameter
Mid-cavity
outlet - 12.5cm AP diameter
What is the purpose of the ischial spines?
Landmarks to assess the descent of the head of vaginal examination.
The level of descent is called ‘station’ - crudely measured in cms in relation to the spines.
Station 0 means the head is at the level of the spines while +2 is 2cm below and -2 is 2cm above
What is cervical dilatation dependent on?
Prerequisite for delivery
dependent on:
contractions
the pressure of the foetal head on the cervix and the ability of the cervix to soften and allow distention
What is the outcome for the soft tissues of the vagina in labour?
Soft tissues need to be overcome - the perineum often tears or is cut (episiotomy) to allow the head to deliver
What are the characteristics of the foetal head prior to delivery?
Head = oblong in transverse section
Bones are not yet fused and spaces between them are palpable as sutures and fontanelles.
The anterior fontanelle (bregma) lies above the forehead - the posterior fontanelle (occiput) lies on the back of the top of the head - between these two is the vertex
In front of the bregma is the brow - because the head is not round, several factors determine how easily it fits through the pelvic diameters
What is the ‘attitude’?
the degree of flexion of the head on the neck: vertex, brow or head
What is the ideal attitude?
The ideal attitude is maximal flexion, keeping the head bowed
this is called vertex presentation and the presenting diameter is 9.5cm running from the anterior fontanelle to below the occiput at the back of the head
What is the effect of extension?
Larger diameter
Extension of 90% causes a brow presentation and a much larger diameter of 13cm
further 30 degree extension = face presentation
Extension of the head can mean that the foetal diameters are too large to deliver vaginally
What is the ‘position’?
The degree of rotation of the head on the neck
What is the significance of ‘position’?
if the saggital suture is transverse, the oblong head will fit the pelvic inlet best - but at the outlet, the saggital suture must be vertical for the head to fit.
The head must therefore rotate 90 degrees during labour.
What is the usual position of delivery?
Usually delivered with the occiput anterior - OA
in 5% deliveries, it may be OP and more difficulty may be encountered.
persistence of the OT position implies non-rotation and delivery without assistance is impossible
What is moulding?
Compression of the head in the pelvis - sutures allow the bones to come together and even overlap.
This slightly reduces the diameters of the head.
What is the effect of pressure of the scalp on the cervix or pelvicinlet?
Localised swelling or caput
Relatively unusually for a normally formed head to be simply too big to pass through the normal bony pelvis
larger head may cause a longer and more difficult labour
What is the presentation?
The part of the foetus that occupies the lower segment or pelvis
head (cephalic) pr buttocks (breech)
What is the presenting part?
the lowest part of the foetus palpable on vaginal examination. The lowest part of the head or breech
For a cephalic presentation, this can be the vertex, the brow or the face, depending on the attitude. For simplicity, these are often described as separate ‘presentations’
What does the position of the head describe?
Rotation: occipito-transverse (OT), occipital-posterior or occipital-anterior OA
when do contractions occur?
Throughout the 3rd trimester - often felt as Braxon hicks contractions
These 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 contraction
How do contractions leading to labour occur?
foetus has a role
prostaglandin production is important for reduction of cervical resistance and increasing release of oxytocin from the posterior pituitary.
This aids stimulation of contractions, which arise in one of the pacemakers situated at each corner of the uterus
When is labour diagnosed?
The signs of labour are:
Show (mucus plug from the cervix)
Rupture of membranes
Regular, painful contractions
Dilating cervix on examination
What is the first stage of labour?
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).
The “show” refers to the mucus plug in the cervix, which prevents bacteria from entering the uterus during pregnancy, falling out and creating space for the baby to pass through.
What are the three phases of the first stage of labour?
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.
What is the second stage?
Lasts from full dilation of the cervix to delivery
What occurs during the second stage?
descent, flexion and rotation are completed and followed by extension as the head delivers
Passive stage
Active stage
What is the passive stage?
Lasts from full dilation until the head reaches the pelvic floor and women experience the desire to push - rotation and flexion are commonly completed.
This stage may last a few minutes, but it can be much longer
What is the active stage?
when the mother is pushing - the presence of the head on the pelvic floor produces an irresistible desire to bear down, although spinal analgesia may present this
How long does the foetus take to be delivered?
about 40 minutes in nulliparous women
20 minutes multiparous women
this stage can be much quicker, but if it takes >1hr, spontaneous delivery becomes increasingly unlikely
How does delivery occur?
As the head reaches the perineum, it extends to come up out of the pelvis
The perineum begins to stretch and often tears, but can be cut if progression is slow of foetal distress is present
The head then restitutes, rotating 90 degrees to adopt the transverse position in which it entered the pelvis. With the next contraction, the shoulder delivers. the anterior shoulder comes under the pubic symphysis first, usually aided by lateral body flection in a posterior direction. The posterior shoulder is aided by lateral body flection in an anterior direction. The rest of the body follows.
What is the third stage of labour?
The time from delivery of the foetus to delivery of the placenta.
It normally lasts about 15 minutes.
Normal blood loss is <500ml
What happens during the third stage of labour?
Uterine muscle fibres contract to compress the blood vessels formerly supplying the placenta, which shears away from the uterine wall.
What are the different types of perineal trauma?
Perineum is intact in about 1/3 of nulliparous women and 1/2 of multiparous women.
Different tears:
1st degree - minor damage to the fourchette
2nd degree and episiotomies - perineal muscle
3rd degree - anal sphincter (1%)
4th degree - anal mucosa
