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Reproductive system > Lecture 20- Physiological labour > Flashcards

Lecture 20- Physiological labour Flashcards

1
Q

labour is the

A

physiological process by which a foetus is expelled from the uterus to the outside world.

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2
Q

how many stages of labour

A

3

characterised by specific physiological changes in the uterus which eventually result in expulsion of the foetus

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3
Q

after expulsion from the uterus the foetus becomes a

A

neonate

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4
Q

Pregnancy ends with the expulsion of the production of conception

*

A
  • Fetus
  • Placenta
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5
Q

If this expulsion occurs after 24 weeks=

A

labour

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6
Q

If it occurs before 24 weeks it is commonly called =

A

spontaneous abortion (miscarriage)

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7
Q

The act of giving birth=

A

parturition

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8
Q

Labour that occurs before the 37th week of gestion =

A

premature or pre-term labour.

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9
Q

Expulsion of the fetus requires a number of processes (first, second and third stages of labour)

A

Creation of a birth canal

Release of the structures which normally retain the fetus in utero

The enlargement and realignment of the cervix and vagina

Expulsion of the foetus

Expulsion of the placenta and changes to minimise blood loss from the mother

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10
Q

intitiation fo labour

A

The exact process by which labour is initiated in humans is not fully understood.

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11
Q

what occurs throughout the third trimester

A

involuntary contractions of the uterine smooth muscle begin to occur – these are known as Braxton Hicks contractions. They occur irregularly and are thought to be a form of “practice contraction”, but they are not regarded as a part of labour.

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12
Q

for labour to commence what has to occur

A
  • The expulsion of the fetus requires a number of processes:
  • The creation of a birth canal
  • The release of the structures which normally retain the fetus
  • in utero
  • The enlargement and realignment of the cervix and vagina (cervical ripening)
  • Expulsion of the fetus
  • Expulsion of the placenta and changes to minimise blood loss from the mother
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13
Q

A woman is typically said to be in labour when

A

when regular, painful contractions lead to effacement and dilatation of the cervix.

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14
Q

Cervical Ripening

A

Cervical ripening refers to the softening of the cervix that occurs before labour. Without these changes, the cervix cannot dilate.

It occurs in response to oestrogen, relaxin and prostaglandins breaking down cervical connective tissue; prostaglandins are of particular importance.

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15
Q

Prostaglandins are produced by the

A

placenta, the uterine decidua, the myometrium and the membranes.

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16
Q

prostaglandin synthesis in the third trimester

A

Their synthesis increases throughout the third trimester as a result of an increase in the oestrogen:progesterone ratio.

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17
Q

Ripening involves:

A
  • A reduction in collagen.
  • An increase in glycosaminoglycans.
  • An increase in hyaluronic acid.
  • Reduced aggregation of collagen fibres.
  • This means that the cervix offers less resistance to the presenting part of the foetus during labour.
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18
Q

myometrial exctiability during initiation of labour

A

The relative decrease in progesterone in relation to oestrogen that occurs towards the end of pregnancy helps to facilitate an increase in the excitability of the uterine musculature. This is because progesterone typically inhibits contractions and oestrogen increases the number of gap junctions between smooth muscle cells, increasing contractility.

Mechanical stretching of the uterus also helps to increase contractility – this means as the foetus grows, the contractility of the muscle increases.

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19
Q

The Role of Oxytocin in initiating labour

A

Oxytocin is responsible for initiating uterine contractions.

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20
Q

why does oxytocin have limited action during pregnancy

A

there are a low number of oxytocin receptors and it is inhibited by relaxin and progesterone.

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21
Q

oestrogen and oxytocin at around 36 weeks gestation

A

under the influence of oestrogen there is an increase in the number of oxytocin receptors present within the myometrium. This means the uterus begins to respond to the pulsatile release of oxytocin from the posterior pituitary gland.

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22
Q

oxytocin feedback

A

one of the only examples of positive feedback- fergusons reflex

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23
Q

oxytocin positive feedback

A

Oxytocin production is increased by afferent impulses from the cervix and vagina. This means that contractions result in a positive feedback loop to the posterior pituitary gland to release more oxytocin, leading to stronger contractions which then drives the process of labour. This is known as the Ferguson reflex.

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24
Q

Stages of labour known as

A

first, second (delivery stage), third stage

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25
Q

The uterus first becomes palpable

A

at around 12 weeks of gestation, by 20 weeks it has reached the level of the umbilicus, by 36 weeks it reaches the xiphisternum.

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26
Q

the first stage of labour results in

A

in the creation of the birth canal and lasts from the beginning of labour until the cervix is fully dilated (~10cm).

Throughout the first stage contractions will occur every 2-3 minutes.

If foetal membranes have not already ruptured, they do during this stage.

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27
Q

first stage can be divided into 2 phases

A

latent phase

active phase

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28
Q

The latent phase –

A

slow cervical dilatation over several hours which lasts until the cervix has reached 4cm dilatation.

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29
Q

The active phase –

A

faster rate of cervical dilatation until 10cm dilatation reached, the typical rate is around 1cm/hr in nulliparous women and 2cm/hr in multiparous women. This phase should not normally last longer than 16 hours.

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30
Q

what does the lie of the foetus describe

A

describes the relationship of the long axis of the fetus to the long axis of the uterus. The commonest lie is longitudinal, with the head or buttocks posterior. The fetus normally has a flexed attitude.

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31
Q

what does the presentation of the fetus desctibe

A

which part of the fetus is adjacent to the pelvic inlet. If the baby lies longitudinally the presenting part may be the head (cephalic) or the breech (podalic).

The presenting part may be in a variety of positions which affects the diameter of presentation.

32
Q

Most commonly, the baby lies

A

longitudinally, in a cephalic presentation, well flexed so that the vertex presents to the pelvic inlet.

33
Q

if the foetus is lieing longitudinallym the diamter of presentation is typically

A

9.5cm

The birth canal therefore needs to have a diameter of about 10cm for the fetus to pass through. This required diameter may change with different positions, e.g. if the fetal head is extended.

34
Q

The Creation of a birth canal…..The birth canal diameter cannot extend beyond the limits determined by the

A

pelvis. Remember, the pelvic inlet is bounded:

  • Posteriorly by the sacral promontory
  • Laterally by the ilio-pectinal line
  • Anteriorly by the superior pubic rami and the upper margin of the pubic symphysis.
35
Q

The true diameter of this inlet is normally about

A

11cm.

36
Q

what allows some expansion of the birth canal to occur

A

Softening of the pelvic ligaments e.g. relaxin

37
Q

outline the creation of a birth canal…

A
  1. the cervix must dilate and be retracted anteriorly.
  2. At some time during this process the fetal membranes rupture, releasing amniotic fluid.
  3. Cervical dilatation is facilitated by structural changes known as cervical ripening, but produced by forceful contractions of uterine smooth muscle.
  4. These contractions first thin the cervix (‘effacement’) and then dilate it.
38
Q

Cervical Softening (or ‘Ripening’)

A

The cervix has a high connective tissue content made up of collagen fibres embedded in a proteoglycan matrix. Ripening involves a marked reduction in collagen and marked increase in glycosaminoglycans (GAGs), which decrease the aggregation of collagen fibres. In consequence collagen bundles ‘loosen’. There is also influx of inflammatory cells, and increase in nitric oxide output. All of these changes are triggered by prostaglandins, namely E2 and F2α.

39
Q

which hormoens trigger cervical ripening

A

All of these changes are triggered by prostaglandins, namely E2 and F2α.

40
Q

uterine smooth muscle during pregnancy

A

During pregnancy, the myometrium gets much thicker due primarily to increased cell size (10 fold) and glycogen deposition. An intracellular apparatus containing actin and myosin, triggered by a rise in intracellular calcium concentration, generates force. The rise in calcium concentration is produced by action potentials in the cell membrane.

41
Q

Action potentials spread from cell to cell via

A

specialised gap functions, allowing co-ordinated contractions to spread over the myometrium. Some smooth muscle cells are capable of spontaneous depolarization and action potential generation, and so can act as ‘pacemakers’.

42
Q

The onset of labour is a relatively sudden increase in the frequency and force of contractions.Two hormones are implicated in this change:

A

prostaglandins

oxytocin

43
Q

porstaglands

A

enchancing the release of calcium from intracellular stores

44
Q

oxytocin and the onset of labour

A

peptide hormone is secreted from the posterior pituitary gland under the control of neurons in the hypothalamus.

It acts by lowering the threshold for trigger the threshold for tirgger APs

45
Q

depiction of crvicla effacement and dilatation during labour

A
46
Q

Uterine smooth muscle has another crucial property –

A

brachystasis.

47
Q

brachystasis

A

At each contraction muscle fibres shorten, but do not relax fully. The uterus, particularly the fundal region therefore shortens progressively. This pushes the presenting part into the birth canal and stretches the cervix over it. Descent of the presenting part (commonly the fetal head) therefore occurs progressively during labour, until it engages in the pelvis.

48
Q

Initiation of Labour

A

All the evidence from animals suggests labour is initiated by an increase in prostaglandin production and oxytocin sensitively triggered by a fall in progesterone levels relative to oestrogen.

49
Q

evidence for a fall in progesterone levels relative to oestrogen role in labour in humans

A

The situation in humans is much less clear. There is no clear evidence of pre-labour increases in plasma prostaglandins or changes in oestrogen progesterone ratio. Prostaglandins will, however, induce labour when given medically.

50
Q

what may lead to a reduction in fetal heart rate as labour progresses

A

increasingly forceful uterine contractions may temporarily reduce placental blood flow, and so reduce oxygen supply to the fetus. This may lead to brief reductions in fetal heart rate that may be monitored. If the reductions in flow are greater than usual larger ‘dips’ occur, as the fetus becomes ‘distressed’.

51
Q

second stage of pregnancy summary

A

This lasts from full dilatation of the cervix until the foetus has been expelled. Uterine contractions become expulsive and this pushes the foetus through the birth canal.

52
Q

2 stages of the second stage of labour

A

passive stage

active stage

53
Q

The passive stage –

A

this lasts until the head of the foetus reaches the pelvic floor, at which point the woman experiences the desire to push. Rotation and flexion of the head are also completed in this stage. It typically only lasts a few minutes.

54
Q

The active stage –

A

the pressure of the foetal head on the pelvic floor results in an urge to “bear down”. During this stage the woman pushes in conjunction with her contractions in order to expel the foetus.

55
Q

The second stage of labour normally lasts up to

A

1 hour in the multiparous woman and up to 2 hours in primigravida (first pregnancies).

56
Q

outline the second stage of labour step by step

A

It typically occurs in the following way:

  1. The descended head flexes as it meets the pelvic floor, reducing the diameter of presentation.
  2. There is then internal rotation.
  3. The sharply flexed head descends to the vulva, so stretching thevagina and perineum.
  4. The head is then delivered (‘crowning’), and as it emerges itrotates back to its original position and extends.
  5. The shoulders then rotate followed by the head, and theshoulders deliver, followed rapidly by the rest of the fetus.
57
Q

myometrium adaptations during the second stages of labour

A

The fibres of the myometrium are specially adapted to drive the process of labour as they do not fully relax following each contraction. This steadily reduces the uterine capacity, so the pressure inside becomes stronger as labour progresses and helps with expulsion of the foetus. Contractions are made more forceful and frequent by the actions of two hormones:

Prostaglandins – more intracellular calcium is released per action potential, increasing the force of contractions

Oxytocin – lowers the threshold for action potentials, increasing the frequency of contractions

58
Q

The second stage of labour ends with

A

delivery of the fetus.

59
Q

shoulder dystocias usually causes what sort of brachial plexus injury

A

Upper brachial plexus injury - Erbs palsy

60
Q

Erb’s palsy involves

i

A

involves the upper portion (C5, C6, and sometimes C7) of the brachial plexus. A child typically has weakness involving the muscles of the shoulder and biceps. Home physical therapy begins when a baby is 3 weeks old to prevent stiffness, atrophy, and shoulder dislocation

61
Q

Total plexus involvement

A

This represents roughly 20 to 30 percent of brachial plexus injuries. All five nerves of the brachial plexus are involved (C5-T1). Children may not have any movement at the shoulder, arm, or hand.

62
Q

Horner’s syndrome

A

This represents roughly 10 to 20 percent of injuries. It is usually associated with an avulsion. The sympathetic chain of nerves has been injured, usually in the T2 to T4 region. The child may have ptosis (drooping eyelid), miosis (smaller pupil of the eye), and anhydrosis (diminished sweat production in part of the face). The child may have a more severe injury of the brachial plexus.

63
Q

Klumpke’s palsy

A

This almost never occurs in babies or children. It involves the lower roots (C8, T1) of the brachial plexus. It typically affects the muscles of the hand.

64
Q
A
65
Q

The Third Stage of Labour

A

With the fetus removed there is a powerful uterine contraction, which separates the placenta, positioning it into the upper part of the vagina or lower uterine segment. The placenta and membranes are then expelled, normally within about 10 minutes. This completes the third stage of labour.

66
Q

what occurs during the third stage of labour to reduce bleeding

A

Contraction of the uterus constricts blood vessels in the myometrium

Pressure is exerted on the placental site once it has been delivered by the walls of the contracted uterus

The normal blood clotting mechanism

67
Q

third stage usually last

A

15 minutes

68
Q

how much blood is lost

A

up to 500 ml normally

69
Q

Within a short time of delivery the fetus takes its first breath, triggered by multiple stimuli

A

delivery trauma, temperature change and others

70
Q

the effect independent breathing has on the babys CVS

A
  1. This causes a dramatic fall in pulmonary vascular resistance, so reducing pulmonary arterial pressure and increasing left atrial pressure relative to right atrial pressure.
  2. The atrial pressure change shuts the foramen ovale, and rising arterial pO2 causes the ductus arteriosus to constrict, so establishing the adult form of circulation. The sphincter in the ductus venosus constricts, so that all blood entering the liver passes through the hepatic sinusoids.
71
Q
A
72
Q

condition of the neonate following delivery is scored by the

A

‘APGAR Score’

This generates a score from 1-10; the higher the number the healthier the baby.

73
Q

Clinically, elements of labour can be classified into

A

“The Powers, The Passage and The Passenger”.

74
Q

The Powers

A

Delivery of the fetus is dependent upon contraction of the myometrium, which has undergone considerable hypertrophy and hyperplasia during pregnancy. Contraction and retraction of the multidirectional smooth muscle fibres causes progressive shortening, particularly in the fundus of the uterus. Uterine contractions can be assessed in terms of frequency, amplitude and duration.

75
Q

The Passage

A

The passage is formed by the bony pelvis and soft tissues. The pelvic inlet is shorter in the anterior - posterior plane (obstetric conjugate, 10.5cm). Between the pelvic inlet and outlet, the mid-cavity is circular (12cm diameter). The pelvic outlet is narrowest usually mediolaterally (11cm). The fetus flexes, extends and rotates as it passes through the birth canal. Resistance of the soft tissue can slow labour.

76
Q

The Passenger

A

The size and presentation of the fetus is critical in labour. The orientation of the head of the fetus when entering the pelvis (in a cephalic delivery) is variable and as such the head diameter of the fetus is different in differing positions. However, moulding of the fetal cranium may occur since cranial sutures have not yet fused.

77
Q

Failure to progress in labour may be due to

A

inadequate power (insufficient uterine contractions)

inadequate passage (abnormal bony pelvis, rigid perineum) and/or

abnormalities of the passenger (fetus too big, fetal presentation).

Progress in labour is plotted graphically on a partogram.

Reproductive system (28 decks)

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