Labour

Question 1

Describe the stages of labour?

Answer 1

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

Question 2

What are the three mechanical factors that determine progress during labour?

Answer 2

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

Question 3

How is power of labour established?

Answer 3

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

Question 4

What are the three principle planes of the bony pelvis?

Answer 4

Inlet - 13cm transverse diameter

Mid-cavity

outlet - 12.5cm AP diameter

Question 5

What is the purpose of the ischial spines?

Answer 5

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

Question 6

What is cervical dilatation dependent on?

Answer 6

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

Question 7

What is the outcome for the soft tissues of the vagina in labour?

Answer 7

Soft tissues need to be overcome - the perineum often tears or is cut (episiotomy) to allow the head to deliver

Question 8

What are the characteristics of the foetal head prior to delivery?

Answer 8

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

Question 9

What is the ‘attitude’?

Answer 9

the degree of flexion of the head on the neck: vertex, brow or head

Question 10

What is the ideal attitude?

Answer 10

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

Question 11

What is the effect of extension?

Answer 11

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

Question 12

What is the ‘position’?

Answer 12

The degree of rotation of the head on the neck

Question 13

What is the significance of ‘position’?

Answer 13

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.

Question 14

What is the usual position of delivery?

Answer 14

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

Question 15

What is moulding?

Answer 15

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.

Question 16

What is the effect of pressure of the scalp on the cervix or pelvicinlet?

Answer 16

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

Question 17

What is the presentation?

Answer 17

The part of the foetus that occupies the lower segment or pelvis
head (cephalic) pr buttocks (breech)

Question 18

What is the presenting part?

Answer 18

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’

Question 19

What does the position of the head describe?

Answer 19

Rotation: occipito-transverse (OT), occipital-posterior or occipital-anterior OA

Question 20

when do contractions occur?

Answer 20

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

Question 21

How do contractions leading to labour occur?

Answer 21

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

Question 22

When is labour diagnosed?

Answer 22

The signs of labour are:

Show (mucus plug from the cervix)
Rupture of membranes
Regular, painful contractions
Dilating cervix on examination

Question 23

What is the first stage of labour?

Answer 23

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.

Question 24

What are the three phases of the first stage of labour?

Answer 24

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.

Question 25

What is the second stage?

Answer 25

Lasts from full dilation of the cervix to delivery

Question 26

What occurs during the second stage?

Answer 26

descent, flexion and rotation are completed and followed by extension as the head delivers

Passive stage

Active stage

Question 27

What is the passive stage?

Answer 27

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

Question 28

What is the active stage?

Answer 28

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

Question 29

How long does the foetus take to be delivered?

Answer 29

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

Question 30

How does delivery occur?

Answer 30

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.

Question 31

What is the third stage of labour?

Answer 31

The time from delivery of the foetus to delivery of the placenta.
It normally lasts about 15 minutes.

Normal blood loss is <500ml

Question 32

What happens during the third stage of labour?

Answer 32

Uterine muscle fibres contract to compress the blood vessels formerly supplying the placenta, which shears away from the uterine wall.

Question 33

What are the different types of perineal trauma?

Answer 33

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