S8) Labour and Delivery Flashcards

1
Q

Define parturition

A

Parturition is transition from the pregnant to the non-pregnant state (birth)

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2
Q

Define labour

A

Labour is the physiologic process by which a fetus is expelled from the uterus to the outside world

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3
Q

Define delivery

A

Delivery is the method of expulsion of the fetus, transforming the foetus to neonate

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4
Q

Identify the 3 stages of labour

A
  • First stage: creation of the birth canal
  • Second stage: descent of foetus and delivery
  • Third stage: delivery of placenta
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5
Q

Describe the first stage of labour physiologically and clinically

A
  • Physiologically: multiple changes resulting in creation of the birth canal and descent of the fetal head
  • Clinically: interval between onset of labour and full dilatation of the cervix
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6
Q

Identify and describe the two phases in the first stage of labour

A
  • Latent: onset of labour with slow cervical dilatation but softening (variable duration)
  • Active: faster rate of change & regular contractions
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7
Q

Describe the second stage of labour physiologically and clinically

A
  • Physiologically: changes in uterine contractions to expulsive, descent of the foetus through the birth canal and delivery
  • Clinically: the time between full (10cm) dilatation of the cervix and delivery
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8
Q

Identify the passive and active efforts involved in the second stage of labour

A
  • Passive – descent and rotation of the head
  • Active – maternal effort to expel the foetus and achieve birth
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9
Q

Describe the third stage of labour physiologically and clinically

A
  • Physiologically: expulsion of the placenta and contraction of the uterus
  • Clinically: starts with completed birth of the baby and ends with complete expulsion of placenta and membranes
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10
Q

How long does the third stage of labour take?

A

Usually lasts between 5 and 15 minutes (may be 30-60 min in certain circumstances)

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11
Q

In 5 steps, describe the mechanism of labour

A

⇒ Head flexion and internal rotation

⇒ Crowning – head stretches through perineal muscle and skin

⇒ Head extension and external rotation

⇒ Shoulders rotate and deliver

⇒ Body rapidly delivers afterwards

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12
Q

How does labour start?

A

Labour is initiated by cervical “ripening” wherein the uterine musculature becomes progressively more excitable

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13
Q

What causes cervical ripening?

A

Cervical ripening is due to oestrogen, relaxin and prostaglandins (PGE2, PGF) breaking down the connective tissue

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14
Q

In 4 steps, describe the physiological process of cervical ripening

A

⇒ Reduction in collagen

⇒ Increase in glycosaminoglycans

⇒ Increases in hyaluronic acid

Reduced aggregation of collagen fibres

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15
Q

What promotes labour in humans?

A

Prostaglandins promote labour

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16
Q

What are prostaglandins and what do they do?

A

Prostaglandins are powerful contractors of smooth muscle and are also involved in cervical softening

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17
Q

Describe the structure, production and control of prostaglandins

A
  • Structure: biologically active lipids (local hormones)
  • Production: placenta, myometrium and decidua
  • Control: production controlled by oestrogen:progesterone ratio
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18
Q

What stimulates prostaglandin synthesis?

A
  • Increase in oestrogen: progesterone ratio and mechanical damage stimulates prostaglandin synthesis
  • Increased synthesis of prostaglandins by amnion in third trimester and prostaglandin levels rise very early in labour
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19
Q

Explain how a rise in the oestrogen:progesterone (relative decrease in progesterone) stimulates myometrial contractility

A
  • Progesterone inhibits contractions
  • Oestrogen increases contractility by increasing gap junctional communication between smooth muscle cells
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20
Q

Describe the function and inhibition of oxytocin

A
  • Oxytocin initiates uterine contraction
  • Inhibited in pregnancy by progesterone, relaxin and a low number of oxytocin receptors
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21
Q

Describe the secretion and control of oxytocin

A
  • Secreted by posterior pituitary
  • Controlled by hypothalamus
22
Q

Describe the processes facilitating the release and action of oxytocin

A
  • Increased by afferent impulses from cervix and vagina (Ferguson reflex)
  • Acts on smooth muscle receptors in myometrium
  • More receptors if oestrogen:progesterone high
23
Q

Cervical effacement and dilation are required to create the birth canal.

What does this involve?

A
  • Dilation is the opening of the cervix (measured in centimeters)
  • Effacement is the thinning of the cervix (measured in percentage)
24
Q

What is the birth canal?

A

The birth canal is the passage through which the foetus passes during birth, formed by the cervix, vagina, and vulva

25
Q

How do we assess the birth canal?

A
  • Look at size of birth canal
  • Normal presentation diameter = 9.5 cm
26
Q

Changes to which structures are necessary to form the birth canal?

A
  • Pelvic floor
  • Vagina
  • Perineum
27
Q

Describe the changes which occur to form the birth canal

A

The stretching of the fibres of the levator ani and the thinning of the central portion of the perineum transforms it to an almost transparent membranous structure

28
Q

Describe the special properties of the uterine smooth muscle which facilitate labour

A
  • Myometrial fibres contract but only partially relax
  • Myometrial muscle does not return to its original size after contraction (retraction)
29
Q

What is the effect of the contraction and retraction of the myometrium during labour?

A

Permanent partial shortening of the muscle fibres leads to a progressive reduction of uterine capacity and a build up of pressure

30
Q

Foetal attitude refers to the relation of the foetal head to the spine.

Identify different some types observed

A
  • Flexed
  • Neutral
  • Extended
  • Hyperextended
31
Q

Foetal lie refers to the relationship between the longitudinal axis of the fetus and the mother.

Identify some different types observed

A
32
Q

Foetal presentation refers to the relationship of presenting part of the foetus to the maternal pelvis.

Identify some different types observed

A
  • Cephalic presentation
  • Breech presentation
  • Shoulder presentation (with transverse lie)
33
Q

Identify 4 ways of inducing labour

A
  • Stimulate release of prostaglandins (membrane rupture)
  • Artificial prostaglandins
  • Synthetic oxytocin
  • Anti-progesterone agents
34
Q

Identify 5 ways in which the physiological state of the foetus can be monitored during labour

A
  • Monitoring the foetus
  • Heart rate patterns
  • Maternal temperature
  • Colour & amount amniotic fluid
  • Scalp capillary pH
35
Q

How can delivery be facilitated by intervention?

A
  • Caesarean section
  • Operative delivery (forceps, vaccuum extraction)
36
Q

In 4 steps, describe the normal processes limiting maternal blood loss after delivery

A

⇒ Powerful contraction/retraction of uterus constrict blood vessels running through the myometrium

⇒ Pressure exerted on placental site by walls of contracted uterus

Placenta separates and descends

Blood clotting mechanism (sinuses and torn vessels)

37
Q

Identify the oestrogen mediated changes in the cervix and pelvis occurring in advancing pregnancy that will facilitate birth?

A
  • Oestrogen mediates cervical ripening
  • Oestrogen relaxes the peritoneal ligaments
38
Q

What is relaxin and what does it do?

A

Relaxin is a hormone produced by the ovary and placenta which acts via collagenase activity to relax the pelvic ligaments and soften the pubic symphysis

39
Q

What postural change might occur during advancing pregnancy by the effect of relaxin?

A

Exaggerated lumbar lordosis due to weight of baby and softening of the ligaments in the vertebrae

40
Q

What anatomical landmark gives an estimate for 20 weeks of gestation?

A

Fundal height

41
Q

What foetal landmark is used to asses foetal head position in the birth canal?

A
42
Q

If an epidural is used in labour for pain relief, what spinal segments are blocked?

A

T10-S4

43
Q

What is a postpartum haemorrhage?

A

A postpartum haemorrhage is the loss of more than 500 ml of blood in the first 24 hours following childbirth

44
Q

What is the most common cause of PPH?

A

Uterine atony

45
Q

Which physiological mechanism exists to prevent PPH?

A

Uterine retraction, placental separation and descent

46
Q

If the uterus is firm on palpation with continuous bleeding, which other causes of PPH should one consider?

A
  • Lacerations to the genital tract
  • Retained placenta
47
Q

What is Sheehan’s syndrome?

A

Sheehan’s syndrome is a state of postpartum hypopituitarism caused by ischaemic necrosis of the anterior pituitary gland due to blood loss and hypovolaemic shock during and after childbirth

48
Q

Why is the posterior pituitary gland unaffected in Sheehan’s syndrome?

A
  • Anterior pituitary gland enlarges during pregnancy and hence needs a greater blood supply so necrosis will have a greater impact
  • Posterior pituitary gland has an alternative blood supply which is richer (more vascularised)
49
Q

In the below diagram, label the structure A and explain which structure will prevent further expulsion of the foetus once the head is delivered.

A

Anterior shoulder is stuck behind pubic symphysis (structure A) which will obstruct delivery

50
Q

Which structure is at risk of damage during the delivery of the foetus in the diagram below?

A

Upper brachial plexus

51
Q

In what position would you expect to find the arm held in an injury of the upper brachial plexus after a traumatic delivery?

A

Erb’s palsy (waiter’s tip):

  • Arm medially rotated
  • Forearm pronated
  • Wrist flexed