18 - Physiological Labour Flashcards

1
Q

At what week gestation can expulsion of the fetus be classified as labour (parturition)?

A

Labour is the process where fetus, placenta and membranes are expelled through the birth canal. Takes around 18hrs

- 24 weeks, before this it is miscarriage

  • Before the 37th week it is pre-term labour
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2
Q

What are the three stages of labour?

A

1st Stage: onset of regular contractions. creation of birth canal, release of structures normally retaining fetus, enlargement and realignment of cervix and vagina. Latent up to 4cm then active then transition at 8cm

2nd stage: Expulsion of the fetus at 10cm

3rd stage: expulsion of the placenta and changes to minimise blood loss from mother

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3
Q

How do we decide how we are going to manage labour?

A
  • The lie, presentation and position of the fetus
  • Baby should lie longitudinally in a cephalic presentation well flexed so diameter of about 9.5cm
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4
Q

What do we mean by the lie and presentation of the fetus?

A

- Lie: relationship of the long axis of the fetus with the long axis of the uterus. commonest lie is longitudinal

- Presentation: which part of fetus is adjacent to pelvic inlet. If baby longitudinal presenting part may be cephalic or podalic (breech)

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5
Q

What is the pelvic inlet bounded by and how big is this area normally?

A

- Posterior: sacral promontory

- Lateral: iliopectinal line

- Anterior: superior pubic rami (pub symphysis)

True diameter is around 11cm but softening of the pelvic ligaments may allow expansion to occur

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6
Q

What happens to the cervix during labour?

A

Cervical softening (ripening)

Reduction in collagen and increase in GAGs to decrease aggregation of collagen fibres so collagen bundles loosen

Influx in inflammatory cells and nitric oxide output, all dilating the cervix

Changes triggered by prostaglandins E2 and F2a

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7
Q

What happens to the uterine smooth muscle in labour?

A
  • Myometrium gets thicker in pregnancy due to increased cell size and glycogen deposition
  • Rise in calcium concentration from action potentials spreading across gap junctions from pacemakers in the smooth muscle so actin and myosin contract
  • Braxton Hicks are when frequency of contractions decreases from every 30 minutes in early pregnancy but high amplitude
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8
Q

What causes onset of labour?

A

- Increased synthesis of prostaglandins: cause release of calcium from intracellular stores

- Increased sensitivity to oxytocin by fall in progesterone: lowers threshold for triggering action potentials

Both work to increase force and frequency of contractions

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9
Q

What is the Ferguson reflex?

A
  • Sensory receptors in cervix and vagina feed back to hypothalamus promoting oxytocin release
  • Positive feedback makes contractions more forceful and frequent
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10
Q

What is brachystasis?

A
  • Uterine smooth muscle contracts but then does not relax fully allowing fundal region to shorten
  • Pushes presenting part into birth canal until it engages
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11
Q

How can we induce labour and why may fetus go into distress during contractions?

A
  • Give prostaglandins
  • Reduction in placental flow during contraction so lowered fetal heart rate
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12
Q

What are the sequence of events in the second stage of labour and how long does it take?

A
  • When cervical dilation is at 10cm, usually 1hr in multiparous and 2hrs in primigravida
    1. Descended head flexes as it meets pelvic floor to reduce diameter of presentation
    2. Internal rotation
    3. Flexed head descends to vulva stretching the vagina and perineum
    4. Head crowns and as it emerges it rotates back to original position and extends
    5. Shoulders rotate followed by head and shoulders are delivered followed by rest of fetus
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13
Q

What happens in the third stage of labour?

A
  • When fetus is removed there is a powerful uterine contraction which separates the placenta
  • Placenta and membranes usually then delivered in 10 minutes
  • Contaction of uterus along with oxytocin drug compresses blood vessels and stops bleeding
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14
Q

What are the first things that happen to the baby when it is born?

A
  • Takes its first breath in response to temperature change and delivery trauma
  • Fall in pulmonary vascular resistance and pulmonary arterial pressure, increasing left atrial pressure. Closes the shunts
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15
Q

What tool is used to assess the wellbeing of a neonate?

A

- APGAR score when initially born and then 5 minutes later

  • Higher number on 1-10 the healthier the baby
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16
Q

What are the three P’s of labour?

A

- Power: uterine contractions which can be assessed by frequency, amplitude and duration

- Passage: birth canal

- Passenger: size and presentation of fetus

Failure of labour to progress can be due to any of these factors. Plot a partogram

17
Q

What are some of the changes that occur 2-3 weeks before labour?

A

Lightening means the head is dropping and may get sharp shooting pains

18
Q

What are the factors needed to mark the onset of labour contractions?

A
  • At least 2 contractions every ten minutes
  • Contractions so painful that you cannot speak
  • Fundal dominance
19
Q

What needs to happen to the cervix before it dilates?

A
  • Effacement in primigravida
20
Q

What is a show?

A

As cervix dilates the mucoid operculum may come away and be streaked with blood

21
Q

What are forewaters?

A
  • Waters in front of the babies head when it engages
  • Next contraction after losing it can be painful
22
Q

What are some physiological changes to the mother during labour?

A
23
Q

What are some the signs of the second stage of labour?

A
24
Q

What are some risk factors for post-partum haemorraghe and what do you need to do when the placenta has been delivered?

A
  • Need to make sure all the placenta is delivered with all the membranes to reduce risk of haemorraghe
25
Q

What is the definition of post partum haemorraghe and how does the body physiologically try to avoid this?

A
  • Loss of more than 500ml of blood after delivery
  • Blood is hypercoagulable, more plasma and uterine contractions
26
Q

At what point in pregnancy would asymmetrical growth restriction occur?

A

Later stages

27
Q

Why does smoking lead to a restriction in O2 delivery to the fetus?

A
  • Carbon monoxide prevents oxygen disocciating from Hb to the fetus
  • Vasoconstriction of the placental vessels
28
Q

What maternal and fetal landmarks are used to asses fetal head position in the birth canal?

A
  • Ischial spines
  • Fontanelles of the baby
29
Q

What is parturition and delivery?

A

Parturition: transition from a pregnancy to a non-pregnancy state

Delivery: method of expulsion of the fetus