Normal Labour

Question 1

How many stages are there to labour, and how are they defined?

Answer 1

Three stages

• First stage: from diagnosis of labour to full cervical dilation
• Second stage: from full cervical dilatation to delivery of the foetus
• Third stage: from delivery of the foetus to delivery of the placentas

Question 2

Describe the first stage of labour

Answer 2

This has a latent and an active phase.

Latent phase: this is up until 4cm dilatation. This can be a rather slow progress

Active phase: 4cm dilatation to 10cm dilatation. We expect this to go at a rate of 1-2cm per hour, depending on parity.

Question 3

Describe the second stage of labour

Answer 3

This has a passive and an active stage.

Passive stage: this is while the head is still high in the pelvis

Active stage: this is with the head reaching the pelvic floor, and active pushing starts.

We expect this entire stage to take 2-3 hours, depending on parity.

Question 4

Describe the third stage of labour

Answer 4

This is the delivery of the placenta. Usually, gentle chord traction is applied, with guarding of the fundus of the uterus (to prevent uterine inversion).

We expect this entire stage to take 15-30 minutes, depending on parity.

Question 5

What triggers labour?

Answer 5

The direct mechanism is unclear, but prostaglandins play an important role. They increase oxytocin release, and promote cervical ripening.

Question 6

How is labour initiated?

Answer 6

It is believed this occurs when pro-pregnancy factors are overwhelmed by pro-labour factors.

Pro-pregnancy factors:

• Progesterone reduces uterine activity
• Nitric oxide
• Catecholamines act as tocolytics

Pro-labour factors:

• Oxytocin
• Oestrogens increase oxytocin sensitivity
• Prostaglandins promote oxytocin release

Question 7

How is the diagnosis of labour made?

Answer 7

• Painful, regular contractions (at around 3-4 in every 10 minutes)
• Effacement of the cervix
• Engagement of the presenting part

Question 8

How does cervical effacement occur?

Answer 8

The cervix has collagen fibres that are broken down by collagenase enzymes, promoted by prostaglandins.

Question 9

How does the head and body travel through the pelvis and cervix to be born?

Answer 9

It enters the pelvic inlet in the transverse position, and the v shaped pelvic floor forces a 90 degree rotation to an anteroposterior position. The shoulders follow in a similar way.

After the head is born, the neck extends to facilitate its full birth. The anterior shoulder is born with downward lateral flexion of the head, and the posterior shoulder afterwards with upwards lateral flexion. The rest of the body follows quite easily.

Mechanisms:

• Engagement: widest part has passed through the inlet
• Descent: result of uterine contractions
• Flexion: full flexion of head in the canal
• Internal rotation: to an OA position
• Extension: of head to be born
• Restitution: to align back with shoulders
• External rotation: of shoulders to be born

Question 10

What is the shortest diameter in the foetal head?

Answer 10

These are 9.5 cm

• Sub-occipito-bregmatic
• Sub-mento-bregmatic

Question 11

What is the longest diameter in the foetal head?

Answer 11

This is 13.5cm

- Occipito-mental diameter

Question 12

What are the measurements of the maternal pelvic inlet?

Answer 12

This is 13cm wide and 12cm long.

Question 13

What are the measurements of the maternal pelvic outlet?

Answer 13

This is 11cm wide and 12.5 cm long.

Question 14

How does the placenta separate from the uterus?

Answer 14

The uterus contracts and the placenta shears off. This may be indicated with a sudden small gush of dark blood and ‘lengthening’ of the chord.

Question 15

What is a partogram?

Answer 15

This is sheet used to monitor the progress of the first stage of labour.

It measures maternal vital signs, foetal heart rate, and cervical dilatation and descent.

Question 16

What is monitored during the first stage of labour, and at what frequency?

Answer 16

• Pulse, hourly
• BP and Temperature, four hourly
• Foetal heart rate, 15 minutes after a contraction

Question 17

What is monitored during the second stage of labour, and at what frequency?

Answer 17

• Pulse and BP, hourly
• Temperature, four hourly
• Foetal heart rate, 5 minutes after a contraction

Question 18

What is monitored during the third stage of labour, and at what frequency?

Answer 18

Vaginal blood loss, and any tears
APGAR score (1, 5 and 10 minutes)

Question 19

What is meconium staining?

Answer 19

It is staining of liquor with meconium, or foetal faeces.

It can happen spontaneously, or in response to foetal hypoxia. It occurs in 15% of term births, and 40% of births at 42 weeks.

It can be indicative of foetal compromise, but an associated normal CTG is reassuring.

It is measured in grades:
1 - good liquor volume, with light staining
2 - reasonable liquor volume, with heavy suspension of meconium
3 - thick undiluted meconium, of ‘pea-soup’ consistency

The higher the meconium staining grading, the higher the likelihood of metabolic acidosis and meconium aspiration syndrome.

Question 20

Describe cardiotocography

Answer 20

This is measurements of the pressure and foetal heart rate. They are usually measured with two abdominal devices strapped to the mother with elastic bands.

Question 21

What is monitored on cardiotocography?

Answer 21

Maternal contractions

Foetal heart rate: normal at 110-160bpm

Variability: from the baseline of the heart rate. +/- 5-10 bpm is normal. Reduced variability in earlier gestations, or periods of sleep.

Accelerations: a normal part of labour where the heart rate increased by >15bpm. There should be 2 in every 15 minutes, lasting longer than 15 seconds.

Decelerations: a reduction in heart rate by 15bpm, lasting longer than 15 seconds. Can be:

• Early: with a contraction, normal
• Late: over 15 seconds after a contraction, indicate acidosis
• Variable: represent chord compression or acidosis
• Shouldered: shows the foetus is coping well

Sustained tachycardia may indicate prematurity, foetal acidosis, maternal pyrexia, or maternal acidosis.

Question 22

How is foetal blood sampled, and what are the indications?

Answer 22

An amnioscope is used to take blood from the scalp. Indications include:

• Persistent late or variable decelerations
• Persistent or prolonged early decelerations
• Persistent foetal tachycardia
• Grade 2/3 meconium staining with any CTG abnormalities
• Prolonged decreased variability

Foetal blood sampling is contra-indicated when the mother has blood borne viruses, the foetus has a bleeding diathesis or is under 34 weeks gestation.

Normal foetal pH is 7.25 (if <7.2 deliver quickly), normal base excess is -6.

Question 23

What is the ABGAR scoring system?

Answer 23

Activity, Pulse, Grimace (reflexes), Appearance and Respiration. It is measured at 1 minute, 5 minutes and 10 minutes after chord clamping.

Each domain is scored either 0, 1 or 2.

Activity: none (0), some flexion (1), active (2)
Pulse: none (0), <100 (1), >100 (2)
Grimace: flaccid (0), some (1), active (2)
Appearance: blue/pale (0), body pink (1), all pink (2)
Respiration: none (0), slow/irregular (1), strong cry (2)

Any score 0-3 is very bad
Any score 4-6 is moderate
Any score 7-10 is excellent

Question 24

What non-pharmacological techniques exist to manage pain during labour?

Answer 24

Support: healthcare practitioner or birthing partner

Environment: music, maternal mobilisation, comfortable positions (squatting, chairs)

Birthing pools: warm baths. Should not be used if mother is on opioids or is drowsy

Education: breathing and relaxation techniques, massage, acupuncture, acupressure, hypnosis

Question 25

What pharmacological techniques exist to manage pain during labour?

Answer 25

Inhaled analgesics:

• Entonox (50/50 oxygen and nitrous oxide)
• Safe, can be used throughout labour and does not cross placenta
• Has limited effects, and can cause nausea, vomiting and drowsiness

Systemic opioid analgesia

• Pethidine or diamorphine IM
• Safe, patient controlled and easy to administer
• Has limited effects, and can cause nausea, vomiting and respiratory distress
• Pethidine not to be used if delivery expected within 2-3 hours

Pudendal analgesia

• Serves the vulva and the perineum
• Used in instrumental delivery

Regional anaesthesia: can be in the subarachnoid or epidural space

Epidurals:

• Injection between L3 and L4 in the epidural space
• This is the most effective analgesia, with few side effects
• They prolong the second stage of labour and have a higher rate of instrumental delivery
• Side effects include hypotension, urinary retention, pyrexia, respiratory depression
• Complications include injecting anaesthetic into CSF causing respiratory paralysis, and spinal headache

Spinal anaesthesia:

• Injection of local anaesthetic into intrathecal space
• Indicated in CS, instrumental delivery and tear repair

General anaesthetic:

• Carries more risk in pregnant women than non pregnant women
• Higher risk of aspiration