Labour Mechanism and Physiology

Question 1

Causes of failure to progress in labour?

Answer 1

1. Related to the powers = inefficient uterine action
2. Related to the passenger = foetal size; disorder of rotation (occipito-transverse, occipito-posterior positions etc.); Disorder of flexion (e.g. brow presentation)
3. Disorders of the passage; cephalo-pelvic disproportion or possible role of cervix

Question 2

Maternal risk factors for failure to progress in labour?

Answer 2

1. Pelvic inflammation
2. Pelvic tumour / fibroid
3. Arcuate or septate uterus
4. Oligohydraminos
5. Placenta praevia
6. Laxity of muscular layer in walls of uterus

Question 3

What is an arcuate uterus?

Answer 3

Uterine cavity displays a concave contour towards the fundus

Question 4

What is a septate uterus?

Answer 4

septum divides the inner portion of the uterus at its midline

Question 5

Foetal RFx for failure to progress in labour?

Answer 5

o Prematurity
o Multiple pregnancy
o Foetal malformation e.g. hydrocephalus
o Intrauterine deaths

Question 6

Mx of women with inefficient uterine contractions?

Answer 6

o Encourage mobility and supportive measures
o Persistently slow progress is Tx by augmentation (artificial strengthening of contractions); a) Initially with amniotomy (deliberately rupturing amniotic sac)
b) If this does not work in dilating cervix after 2 hours, then oxytocin is given, after malpresentation has been excluded

Question 7

Mx of foetuses that are malpresenting?

Answer 7

o Rotations OP baby to OA using ventouse or manual rotation
o OT delivered using a ventouse
o Brow presentation = c-section
o Face presentation = c-section

Question 8

What is cervical ripening?

Answer 8

• This describes the process by which the cervix goes from a closed, firm structure to a softer, thinner one that opens up adequately for birth
• Occurs before the onset of labour, in the weeks/days predating labour
• It is a more accelerated phase characterised by maximal loss of tissue compliance and integrity
• Upon initiation of uterine contractions, the ripened cervix can dilate sufficiently to allow passage of the foetus
• Effacement is when the normally tubular cervix (like a long bottleneck, up to 4cm in length) is drawn up into the lower segment until it is flat (loss of collagen and elastic tissues)

Question 9

Where are the pacemakers of the uterus?

Answer 9

In the cornu

Question 10

What are the phases of labour?

Answer 10

1. Stage 1 (made up of latent and active stages)
2. Stage 2
3. Stage 3

Question 11

What is the latent phase of labour?

Answer 11

When the cervix dilates up to 3cm

Question 12

What is the active phase of labour?

Answer 12

From 3 to 10cm (fully) dilated

Question 13

What is the average rate of dilation in the active phase?

Answer 13

0.5cm/hour for nulliparous women or 1cm/hour for multiparous women

Question 14

What happens in the 2nd stage of labour?

Answer 14

From full dilatation of the cervix to delivery of the foetus

Question 15

What happens in the 3rd stage of labour?

Answer 15

From delivery of the baby to delivery of the placenta

Question 16

How long does the 2nd stage usually take?

Answer 16

40 mins for nulliparous women, 20 mins for multiparous women (>1 hour makes spontaneous labour less likely)

Question 17

What are the mechanisms that occur in labour?

Answer 17

1. Descent into the pelvis (baby is in transverse position to get through the pelvic inlet)
2. Flexion of the baby (should be fully flexed, with the chin down to the body)
3. Internal rotation (foetal head turns towards the posterior wall as it reaches the pelvic floor)
4. Extension (the foetal head extends beneath the suprapubic arch allowing the head to be born)
5. Restitution / external rotation (the head turns back to the transverse position once it is outside of the woman, so that it is back in line with the rest of the body, allowing this to be born)

Question 18

What are the 3 factors that are key participants in labour?

Answer 18

1. Powers = the degree of force expelling the foetus
2. The passage = the dimensions of the pelvis and the resistance of the soft tissues
3. The passenger = diameters of the foetal head

Question 19

In active labour, how much does the uterus contract?

Answer 19

45-60 seconds about every 2-4 minutes

Question 20

What is the bregma?

Answer 20

The anterior fontanelle, (above the forehead)

Question 21

What is the occiput?

Answer 21

The posterior fontanelle (on the back of the top of the head)

Question 22

What is moulding?

Answer 22

Head can be compressed in the pelvis because sutures allow the bones to come together and even overlap slightly

Question 23

What is a partogram?

Answer 23

• Partogram is used to record progress in dilatation of cervix and descent of the head
• Assessed on vaginal examination and plotted against time
• After the latent phase (i.e. >4cm dilated), usual minimum rate of dilatation is 1cm/hour
• Also monitor foetal heart rate (for foetal distress), maternal pulse, BP and temperature

Question 24

What is foetal distress?

Answer 24

Foetal hypoxia that might result in foetal damage or death if not reversed or the foetus delivered urgently

Question 25

What are the maternal consequences of failure to progress in labour?

Answer 25

• Higher chance of operative delivery
• Infection of uterus
• Damage to birth canal
• Postpartum infection
• Postpartum haemorrhage

Question 26

What is the normal position for labour?

Answer 26

Vertex position. Highest part of foetal head arrives at the pelvic brim first. Chin is tucked down into chest. Occipito-anterior position, when back of babies skull points to the pubic symphysis. 95% occur this way.

Question 27

What is a breech position?

Answer 27

Foetus lies with buttocks in lower part of uterus and its buttocks and/or feet are the presenting parts during delivery. 3-4% after 34 weeks (at term). 25% before 34 weeks

Question 28

Can breech position be delivered normally?

Answer 28

Yes; but it is higher risk

Question 29

RFx for breech position?

Answer 29

1. Obstructive placenta
2. Multiple pregnancy
3. Premature labour (baby may not have turned yet)
4. Polyhydraminos (nothing to hold the baby in face)
5. Abnormal uterus formation
6. Hydrocephaly

Question 30

What are the 3 types of breech?

Answer 30

1. Complete breech (baby is sitting, legs flexed)
2. Frank breech (baby is doubled up on itself; legs extended)
3. Footling breech (one of both of legs hanging down; baby is stood up)

Question 31

How to turn the baby around when breech?

Answer 31

Turn the baby using ECV by pressing on the abdominal wall

Question 32

What happens in a face presentation?

Answer 32

baby’s neck is so completely extended that the occiput at the back of the foetal skull touches baby’s own spine. Chin will present first. 1 in 500 pregnancies. Also called a mento-anterior or mento-posterior (mentum is chin bone). Anterior can be delivered vaginally, but not posterior

Question 33

What is a brow presentation?

Answer 33

baby’s head only partially extended at neck, so brow is presenting part. 1 in 1000 pregnancies. Must be delivered by c-section

Question 34

What is meconium?

Answer 34

Amniotic fluid stained with babies’ faeces

Question 35

Is meconium worrying?

Answer 35

Can be a sign of foetal distress if very thick, but can be fine. Not worrying at all in breech position

Question 36

Initial Mx of a woman that fails to progress in labour?

Answer 36

1. ABC, hydration, pulse, ketotic state
2. Abdo exam (check for breech position)
3. Vaginal exam (confirm dilatation, see how high head is, rotation of head, cervical dilatation for obstructed labour, head compression)
4. Analgesia
5. Can artificially rupture membrane

Question 37

Which factors influence mode of delivery?

Answer 37

1. Maternal distress
2. Foetal distress
3. Obstruction