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Obstetrics > Definitions, Mechanisms, and Diagnosis of Labour > Flashcards

Definitions, Mechanisms, and Diagnosis of Labour Flashcards

1
Q

What is labour also known as?

A

Parturition

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2
Q

What is the definition of labour?

A

The process whereby the products of conception are expelled from the uterine cavity after the 24th week gestation

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3
Q

What is ‘term’ labour?

A

When labour occurs between 37-42 weeks

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4
Q

What percentage of mothers deliver at ‘term’?

A

93-94%

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5
Q

What is pre-term labour?

A

When labour occurs from 24-36+6 weeks

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6
Q

What percentage of mothers deliver pre-term?

A

7-8%

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7
Q

What is it called when the contents of the uterus are delivered before 24 weeks?

A

Miscarriage

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8
Q

Why is miscarriage different to labour?

A

The fetus is not viable (although som pre-term births may not survive either)

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9
Q

What is prolonged labour in primigravida?

A

> 24 hours

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10
Q

What is prolonged labour in multigravida?

A

> 16 hours

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11
Q

What is prolonged labour associated with?

A

Increased fetal and maternal morbidity and mortality

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12
Q

What happens before labour?

A

Pre-labour phase

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13
Q

How long can the pre-labour phase last?

A

Days - weeks

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14
Q

How is labour divided in clinical management?

A

Into 3 stages

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15
Q

What are the three stages of labour called?

A
  • First stage
  • Second stage
  • Third stage

Imaginative isn’t it

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16
Q

What marks the start of the first stage of labour?

A

Onset of regular painful contractions and cervical changes

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17
Q

What marks the end of the first stage of labour?

A

When the cervix reaches full dilation and is no longer palpable

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18
Q

What can the first stage of labour be further divided into?

A
  • Early latent phase

- Active phase

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19
Q

What happens in the early latent phase of the first stage of labour?

A

Cervix becomes effaced and shorter from 3cm in length and dilates up to 3 cm

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20
Q

What happens in the active phase of the first stage of labour?

A

Cervix dilates from 3cm to full dilation (or 10cm)

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21
Q

What marks the start of the second stage of labour?

A

Full cervical dilation

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22
Q

What marks the end of the second stage of labour?

A

Delivery of the fetus

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23
Q

What can the second stage of labour be divided into?

A
  • Pelvic or passive phase

- Active phase

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24
Q

What happens in the pelvic/passive phase of labour?

A

The head descends from the pelvis

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25
Q

What happens in the active phase of labour?

A

The mother gets a stronger urge to push and the foetus is delivered by the force of the uterine contractions and maternal bearing down

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26
Q

What happens in the third stage of labour?

A

Delivery of the placenta and membranes

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27
Q

What hormonal changes take place to initiate the onset of labour?

A
  • Progesterone withdrawal
  • Increase in oestrogen
  • Increase in prostaglandin action
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28
Q

What is likely to be involved in regulating the hormonal changes that naturally induce labour?

A

Corticotrophin-releasing hormone (CRH)

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29
Q

Where is CRH produced?

A

Placenta

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30
Q

Where is CRH produced?

A

Syncitiotrophoblasts

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31
Q

What happens to the number of syncitiotrophoblast nuclei throughout gestation?

A

Increase

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32
Q

What is the effect of the number of syncitiotrophoblast nuclei increasing during gestation?

A

There is an exponential increase in the levels of maternal and fetal plasma CRH

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33
Q

What are the effects of CRH on the placenta?

A
  • Increases production of oestrogen

- Decreases production of progesterone

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34
Q

What is the effect of CRH on the membranes?

A

Increased synthesis of prostaglandins

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35
Q

What molecule is increased by the changes in prostaglandin, progesterone and oestrogen levels throughout pregnancy?

A

Connexin 43

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36
Q

What does connexin 43 promote?

A
  • Connectivity of the uterine myocytes

- Increases myocyte excitability

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37
Q

What is the result of connexin 43’s effects on the uterine myocytes?

A

Generalised uterine contractions

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38
Q

How do contractions of uterine myocytes differ to striated muscle contraction?

A

They shorten and remain so (striated muscle returns to normal length upon relaxation)

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39
Q

What other placental hormones can affect myometrial contraction?

A
  • Relaxin
  • hCG
  • Activating A
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40
Q

Why is the integrity of the cervix essential throughout gestation?

A

To retain the products of conception

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41
Q

What cells are found in the structure of the cervix?

A

Myocytes and fibroblasts

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42
Q

How does the integrity of the cervix change towards term?

A

It becomes soft and stretchable

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43
Q

What causes the cervix to become soft and stretchable towards term?

A

Increase in leukocyte infiltration and a decrease in the amount of collagen due to increased proteolytic enzyme activity

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44
Q

What changes to the connective tissue of the cervix cause softening and stretching?

A

Increased hyaluronic acid to reduce affinity of fibronectin for collagen

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45
Q

What is the softening and stretching of the cervix called?

A

Ripening of the cervix

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46
Q

What changes to cervical and uterine physiology are required in labour?

A
  • Reduced cervical resistance

- Increased frequency, duration and strength of uterine contractions

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47
Q

Are contractions present in pregnancy before labour?

A

Yes

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48
Q

Describe the pre-labour contractions experienced throughout pregnancy?

A

Painless and irregular

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49
Q

How do pre-labour contractions progress throughout pregnancy?

A

They are minimal at the start and become more frequent as pregnancy progress towards labour

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50
Q

What is uterine contractile activity regulated by?

A

The fetoplacental unit

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51
Q

What causes the increased contractile activity at the end of gestation?

A

Down-regulation of factors that keep the uterus and cervix inactive and upregulation of procontractile influences

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52
Q

What is the result of the changes in uterine contractile activity at the end of gestation?

A

Increased frequency, duration and strength of contractions

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53
Q

What is the effect of progressive uterine contractions on the cervix in labour?

A

Causes effacement and dilatation

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54
Q

What happens to the upper uterine segment in labour?

A

There is shortening of the myometrial fibres

55
Q

What happens to the lower uterine segment in labour?

A

Stretching and thinning

56
Q

What happens to the junction between the upper and lower uterine segments in labour?

A

It rises within the abdomen

57
Q

What may happen to the upper and lower uterine junction if labour becomes obstructed?

A

It may become visible at the level of the umbilicus

58
Q

What is it called when the uterine junction is visible in obstructed labour?

A

A retraction ring

59
Q

Where do contraction impulses start and move in the uterus?

A

In the fundal region and spread downwards through the myometrium

60
Q

Where are uterine contractions stronger and longer?

A

At the fundus

61
Q

Why is fundal dominance in uterine contractions important for labour?

A

It allows for progressive effacement and dilatation of the cervix

62
Q

What happens as the uterus and round ligament contract in labour?

A

The axis of the uterus straightens and pulls the longitudinal axis of the foetus towards the anterior abdominal wall in line with the inlet of the true pelvis

63
Q

Why is it important that the axis of the uterus and foetus align with the inlet of the true pelvis?

A

To promote descent of the presenting part as the foetus is pushed into the pelvic cavity

64
Q

What does the bony pelvis consist of?

A
  • Ilium
  • Ischium
  • Pubis
  • Sacrum
  • Coccyx
65
Q

What are the ilium, ischium and pubis known as?

A

The paired innominate bones

66
Q

What joins the innominate bones anteriorly?

A

Symphysis pubis

67
Q

What do the innominate bones articulate with posteriorly?

A

Sacrum

68
Q

What is the joint between the sacrum and the innominate bones known as?

A

The sacroiliac joint

69
Q

What does the sacrum articulate with superiorly and inferiorly?

A
  • 5th Lumbar vertebrae

- Coccyx

70
Q

What is the bony pelvis divided into?

A
  • False pelvis

- True pelvis

71
Q

What separates the false and true pelvis?

A

The pelvic brim

72
Q

What is the true pelvis divided into?

A
  • Pelvic inlet
  • Mid-pelvis
  • Pelvic outlet
73
Q

What is the anterior border of the pelvic inlet?

A

Superior surface of the pubic bones

74
Q

What is the posterior border of the pelvic inlet?

A

Promontory and alae of sacrum

75
Q

Where is the mid-pelvis?

A

At the level of the ischial spines

76
Q

What is the anterior border of the pelvic outlet?

A

Lower border of the symphysis

77
Q

What forms the lateral border of the pelvic outlet?

A

Ischial tuberosities

78
Q

What forms the posterior border of the pelvic outlet?

A

Tip of the sacrum

79
Q

How do the pelvic joints adapt during labour?

A

There is softening of the sacroiliac ligaments and pubic symphysis

80
Q

What does softening of the pelvic joints in labour allow?

A

Expansion of the pelvic cavity

81
Q

How does the fetus adapt to allow the progress of labour?

A

There is changes of the head diameter through flexion, rotation and moulding

82
Q

How do the soft tissues of the pelvis adapt to labour?

A

They are more distensible to help reduce the risk of tearing of the perineum and vaginal walls during birth of the head

83
Q

What pelvic soft tissues become more distensible in labour?

A
  • Pelvic floor
  • Vaginal orifice
  • Perineum
84
Q

In which diameter is the pelvic inlet larger?

A

Lateral

85
Q

What does the larger lateral pelvic inlet diameter promote?

A

The head to engage in the pelvis in the transverse position

86
Q

Why does passage of the head and trunk in delivery follow a well-defined pattern?

A
  • The upper pelvis strait is transverse
  • The middle pelvic strait is circular
  • The outer pelvic strait is anteroposterior
87
Q

In what percentage of cases does the fetal head present by the vertex?

A

95%

88
Q

What are the processes involved in the fetal head adapting to the various segments of the pelvis?

A
  • Descent
  • Flexion
  • Internal rotation
  • Extension
  • Restitution
  • External rotation
  • Delivery of the shoulders
89
Q

Why is descent an important process of delivery?

A

It is a prerequisite for birth of the baby

90
Q

When does engagement (full descent) of the head occur in most primigravid women?

A

Before the onset of labour

91
Q

When may engagement of the head not occur before labour?

A

In multifarious women

92
Q

When does flexion of the head occur in labour?

A

As it descends and meets the medially and forward sloping pelvic floor

93
Q

What is flexion of the fetal head in labour?

A

Where the chin is brought into contact with the fetal thorax

94
Q

How does flexion affect the diameter of presentation?

A

It provides the smallest diameter by changing from occipito-frontal diameter to suboccipitobregmatic diameter

95
Q

What is the average occipito-frontal diameter?

A

11.5cm

96
Q

What is the average suboccipitobregmatic diameter?

A

9.5cm

97
Q

When does internal rotation of the head occur in labour?

A

When the head reaches the pelvic floor

98
Q

What happens in internal rotation of the head in labour?

A

The occiput rotates anteriorly from the lateral position towards the pubic symphysis

99
Q

What causes internal rotation of the head in labour?

A

Force of contractions being transmitted via the fetal spine to the head at the point where the spine meets the skull

100
Q

When does the head extend in labour?

A

As the base of the occiput comes into contact with the inferior rami of the pubis

101
Q

When does maximal distension of the periueum and introitus occur?

A

During final expulsion of the head

102
Q

What is ‘crowning’ in labour?

A

When the head is seen at the introitus and does not recede between contractions

103
Q

What is restitution of the head in labour?

A

Rotation back into line with the normal relationship to the fetal shoulders after delivery of the head

104
Q

When does external rotation of the fetal head occur in labour?

A

As the shoulders reach the pelvic floor and they rotate into the anteroposterior diameter of the pelvis

105
Q

What is external rotation of the head in labour?

A

When the head accompanies the shoulders to take the anteroposterior diameter of the pelvis to look laterally at the maternal thigh

106
Q

When does final expulsion of the fetal trunk occur in labour?

A

Upon delivery of the shoulders

107
Q

Which shoulder is delivered first in labour?

A

Anterior shoulder

108
Q

How is the anterior shoulder delivered?

A

Traction posteriorly on the fetal head so it emerges under the pubic arch

109
Q

How is the posterior shoulder delivered?

A

Lifting the head anteriorly over the perineum

110
Q

What occurs after the delivery of the shoulders?

A

Rapid delivery of the remainder of the trunk and lower limbs

111
Q

What happens in the third stage of labour?

A

The uterine muscle contracts, shears off the placenta and pushes it into the lower segment and vault of the vagina

112
Q

Why can determining the onset of labour be difficult?

A

Contractions may be irregular and may start and stop with no cervical change

113
Q

What is contractions without cervical change called?

A

‘False labour’

114
Q

How is the duration of labour determined?

A
  • Progress of contractions
  • Cervical changes
  • Descent of the head
115
Q

What are the clinical signs of the onset of labour?

A
  • Regular, painful contractions
  • Passage of blood-stained mucus from the cervix
  • Rupture of fetal membranes
116
Q

How do the contractions of labour change as it progresses?

A

Become more frequent and longer, producing progressive cervical dilation

117
Q

What is the passage of blood stained mucus from the cervix in labour called?

A

The ‘show’

118
Q

Is the ‘show’ on its own an indicator of labour?

A

No

119
Q

When does rupture of fetal membranes occur?

A

Can be at onset but may vary

120
Q

What is PROM?

A

Pre-labour rupture of membranes?

121
Q

What is the definition of PROM?

A

Rupture of membranes followed by a latent period of > 4 hours before onset of painful contractions

122
Q

What is it called if PROM happens in the pre-term period?

A

Pre-term pre-labour rupture of membranes (PPROM)

123
Q

How can the request and duration of contractions be determined?

A

By palpation or external tocography

124
Q

What is needed to assess the strength of contractions in labour?

A

Intrauterine pressure catheters

125
Q

What frequency of contractions suggests labour has started?

A

Two contractions of >20 seconds in 10 minutes

126
Q

What is the normal resting tonus in labour?

A

~10-20 mmHg

127
Q

What happens to the normal resting tonus as labour progresses?

A

It increases slightly

128
Q

What happens to the intensity of contractions throughout labour?

A

They increase

129
Q

Where should contractions be recorded?

A

On the partograph

130
Q

How are contractions recorded in the partograph?

A

Based on frequency and duration

131
Q

What are the classical signs of placental separation seen in the third stage of labour?

A
  • Trickling of bright blood
  • Lengthening of the umbilical cord
  • Elevation of the uterine fundus with the abdominal cavity
132
Q

How long does the third stage of labour usually take?

A

5-10 minutes

133
Q

When is a diagnosis of a retained placenta made?

A

If not expelled within 30 minutes

134
Q

Is a retained placenta a sign of normal third stage labour?

A

No, it’s abnormal. This seems a bit obvious tbh

Obstetrics (61 decks)

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