8.1 Parturition

Question 1

What is the definition of labour?

Answer 1

Expulsion of products of conception after 24weeks

Question 2

Define the following timelines:

spontaneous abortion
pre-term
term

Answer 2

Spontaneous abortion: before 24 weeks
pre-term: before 37 weeks
Term:37 – 42 weeks

Question 3

What are the 3 stages of labour? Include any substages that may occur

Answer 3

1) First Stage: Interval between the onset of labour and full cervical dilation AND creation of the birth canal
Two phases:

• Latent phase: onset of labour with slow cervical dilationton ~4 cm and variable duration
• Active phase: faster rate of cervical change, 1- 1.2cm/hour, regular uterine contractions

2) Second Stage: delivery of the foetus
3) Third Stage: delivery of the placenta

Question 4

What are the 3 important P’s that should be considered during labour?

Answer 4

1) Powers
2) Passenger
3) Passage

Question 5

At what week is a womens first dating scan, give one purpose of this

Who usually monitors birth and where is the information kept

Answer 5

Week 12: identifies single or or multiple birth

Growth of foetus monitored by midwife and plotted on individualised growth charts

Question 6

During pregancy (before labour) when would the uterus be palpable?

During weeks 20 and 36 where should it be palpable

Answer 6

Foetus, placenta, uterus increase dramatically in size

Uterus palpable by 12 weeks

Reaches umbilicus by 20 weeks

Xiphisternum by 36 weeks

Question 7

What is meant by the “lie” and “presentation” of foetus towards the end of pregnancy

Describe the classic presentation

Answer 7

Lie: relationship to long axis of uterus

• normally longitudinal and foetus normally flexed

Presentation: which part is adjacent to pelvic inlet

• normally head (cephalic)
• sometimes buttocks (podalic)

Most commonly baby is in a longituidal lie with a cephalic presentation

Question 8

State one other “lie” foetus may be in and describe the appearance of the women

Answer 8

If foetus is in a transverse lie, the long axis of the foetus is at a right angle to the long axis of the mother. The womens abdomen has a wide, short appearance

Question 9

In a normal presentation what is the biggest part of the baby?

What determines the maximum size of the birth canal?

Answer 9

The head (9.5cm)

Max size of birth canal determined by pelvis

• The true diameter of this inlet is normally about 11cm
• Softening of ligaments may increase it

Question 10

Describe the boundaries of the pelvic inlet

Answer 10

pelvic inlet boundries 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

Question 11

Give the 4 types of cephalic presentation and state which one is normal and which 3 are classified as malpresentation

How would each would be delivered

Answer 11

1) Vertex: NORMAL
* Baby’s neck is in complete flexion
2) Sinciput:
* Baby’s neck is partially extended
3) Brow:

• Baby’s neck is extended (diameter is greater than the pelvic inlet and as a result obstructed labour will occur)
• requires C-section

4) Face:

• Baby’s neck is hyper-extended (various reason eg. tumour, anencephaly)
• mento-anterior position = delivered vaginally
• mento-posterior position = C section may be required

Question 12

What is meant by a “breach” and what are the 3 types

What are the options for delivery?

Answer 12

Ideally foetus will be in the cephalic position with a longitudinal lie however, sometimes the foetus is in a podalic presentation (presenting part = buttocks) this is classed as a “breach”

3 types:

1) Franks breach: hips are flexed and knees are extended
2) Full breach: hips and knees are flexed
3) Single footing breach: hips and knees are flexed but foot is the presenting part

Female may be offered at 37 weeks for baby to to be turned OR may be offered a C-section

Question 13

The first stage of labour involves creation of the birth canal, explain the 2 changes that must occur

Answer 13

1) expansion of the soft tissues to around 10cm and the cervix must also retract anteriorly for this to happen
* Soft tissues: cervix, vagina, perineum
2) structural changes: ‘cervical ripening’ and myometrium changes

Question 14

What is ‘cervical ripening’?

Answer 14

The cervix has a high CT content made up of collagen fibres embedded in a proteoglycan matrix. In order for foetus to be expelled we require ripening of these fibres

Ripening involves:

• a marked reduction in collagen
• increase in glycosaminoglycans (GAG’s) which decrease the aggregation of collagen fibres

This causes the collagen bundles to ‘loosen’.

All of these changes are triggered by prostaglandins

Question 15

Name 2 prostaglandins involved in cervical ripening

Answer 15

E2 and F2x

Question 16

Explain the difference between Cervical effacement vs. Cervical dilation

Answer 16

Cervical effacement: the thinning of cervix
Cervical dilation: opening of the cervical oss

Question 17

What causes effacement to occur and what is the ideal amount (%) we want for delivery?

What causes dilation to occur and what is the ideal amount we want for delivery?

Answer 17

Cervical ripening progressively causes cervix to become thinner and softer (effacement), this will also occur due to and increasing regularity and force of contractions

As the cervix become effaced, this is described as a percentage (thinner the cervix = increased
percentage of effacement), ideally best delivery will occur at 100% effacement

As the cervix gets softer and thinner it is more easily able to dilate with the contractions. When cervix reaches 10cm it is classed as fully dilated

Overall ideal delivery occurs at 100% effacement and 10cm fully dilated

Question 18

Describe the structural changes that occur to the myometrium during pregnancy

Answer 18

Myometrium (SM. bundles) thickens during prgnancy due to increased cell size and glycogen deposition, essential to generate the force required to expel the foetus.

Question 19

How is the force of contraction generated within the myometrium? (2)

Answer 19

The FOC originates from an intra-cellular apparatus of actin and myosin, controlled by a rise in intracellular Ca2+.

The intracellular Ca2+ is caused by action potentials across the cell membrane. These action potentials are able to dissipate across the myometrium through specialised gap junctions in the smooth muscle cells. Some smooth muscle cells are able to depolarise and generate AP’s spontaneously acting as “pacemakers” in the uterus

Question 20

What is meant by Brachy stasis?

Answer 20

The myometrium is also able to contract and only partially relax resulting in permanent partial shortening of the muscle fibres after each contraction, this is known as Brachy stasis and is important during labour for expulsion of the foetus

Question 21

Explain the amplitude and timing of uterine contractions during early to late pregnany

Answer 21

Uterine contractions occur throughout pregnancy

Early: low amplitude, more frequent every 30 min

Late: higher amplitude, less frequent

• ‘Braxton-Hicks’ contractions may also occur

Question 22

What are the 2 goals of uterine contractions?

Answer 22

1) To dilate cervix
2) To push the foetus through the birth canal

Question 23

What are ‘Braxton-Hicks’ contractions?

Answer 23

Braxton Hicks contractions are a intermittent tightening of the uterine muscles (1-2mins) and are often infrequent, irregular, and involve only mild cramping

Also known as “False labour”

Question 24

The FOC is wave like, what does this mean?

Answer 24

They incrementally get stronger in intensity until they reach a peak amplitude and then decreases at the same rate until the uterus relaxes. This continues repeating

Question 25

List 2 factors that control contractions ie. increase force and frequency

Answer 25

1) Prostaglandins
* increases Ca2+ release from SM cells per AP
2) Oxytocin
* lowers the AP threshold (more APs occur at a lower threshold)

Question 26

What are prostaglandins, where are they produced and what controls this?

Give 2 functions of these and state one other hormone that may stimulate their release

Answer 26

Biologically active lipids that act as local hormones.

They are produced mainly in endometrium and their production is controlled by oestrogen/progesterone ratio

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

Prostaglandins may also be stimulated by oxytocin

Question 27

State what the effect the following oestrogen/progesterone ratios would have on prostaglandin synthesis:

1) If progesterone is high relative to oestrogen
2) a fall in progesterone relative to oestrogen
3) a rise in oestrogen relative to progesterone

State to overall rule

Answer 27

1) oestrogen/ ⬆progesterone = ⬇ prostaglandin synthesis
2) oestrogen/ ⬇progesterone = ⬆ prostaglandin synthesis
3) ⬆oestrogen/ progesterone = ⬆ prostaglandin synthesis

oestrogen > progesterone = HIGH prostaglandins synthesis

progesterone > oestrogen = LOW prostaglandin synthesis

Question 28

A relative fall in progesterone will have what 3 effects?

Answer 28

1) Increases prostaglandins
2) Ripen cervix
3) Promote uterine contractions

Question 29

Where is Oxytocin secreted from and what control is it under?

What increases its secretion?

Where does it act?

Answer 29

Secreted by posterior pituitary under neuroendocrine control of the hypothalamus

Increased by afferent impulses from Cervix and vagina

• ‘Ferguson reflex’

Acts on smooth muscle receptors

• More receptors if oestrogen/progesterone ratio high

Question 30

What is the effect of high progesterone (low o/p ratio) on oxytocin?

What is the effect of low progesterone (HIGH o/p ratio) on oxytocin and when would this be seen?

Answer 30

Action of Oxytocin is inhibited by the levels of progesterone. This is because a low o/p ratio means the number of receptors within the myometrium will be low

At around 37 weeks the levels of progesterone fall and there is a relative increase in levels of oestrogen. This results in more receptors produced in the myometrium, making cells more sensitive to low circulating levels of the Oxytocin.

Oxytocin acts by binding to receptors on uterine smooth muscle cells to increase the number of contractions. It can also stimulate production of prostaglandins

Question 31

Give two substances that would be increased if there were a HIGH oestrogen/progesterone

Answer 31

1) Prostaglandin synthesis
2) Increase Oxytocin receptors on SM cells (increased oxytocin action)

Question 32

Explain the Ferguson Reflex and state why it is so important

Answer 32

As contractions increase, the ‘Ferguson Reflex’ increases oxytocin secretion massively (positive feedback). This is crucial in continuation of powerful forceful contractions required to expel foetus during labour

Ferguson Reflex:

1) sensory receptors in the cervix and vagina are stimulated by contractions
2) Excitation passes via afferent nerves to the hypothalamus, promoting massive oxytocin release
3) this ‘positive feedback’ makes contractions more forceful and frequent (because of oxytocin)
4) There is also a further increase in prostaglandin secretion (because of oxytocin)
5) sensory receptors are furthur stimulated and the cycle continues

Question 33

What is meant by “breaking of the water”

Answer 33

This is rupture of the amnion caused by increasing cervical dilation

Question 34

How can we induce labour and what çan be used to identify whether this may be required?

Answer 34

Artificial initiation of uterine contractions prior to spontaneous onset resulting in the delivery of the baby

Assess readiness of the cervix using Bishopscore

The more soft, dilated and begging to efface the cervix is = the higher the Bishops score (the more favourable the cervix will be to be induced)

Question 35

Give 3 maternal and 3 foetal factors that suggest we may be required to induce labour

Answer 35

Maternal:

• Severe preeclampsia
• Recurrent antepartum haemorrhage
• Pre-existing disease (diabetes)

Foetal:

• Prolonged pregnancy (most common in UK)
• Intrauterine growth restriction
• Rhesus disease

Question 36

Give 3 methods that can be used to induce labour and explain each (include risks/complications if relevant)

Answer 36

1) Prostaglandins

• Locally applied PE2 as vaginal gel, tablet or pessary
• Ripens cervix and reduces incidence of operative delivery
• dose must be accurate to reduce risk of hyperstimulation of uterus

2) Oxytocin

• IV infusion of synthetic oxytocin
• Requires post-amniotomy care or SRMO
• Requires careful dose titration in accordance with frequency and strength of contrations
• Requires constant fetal monitoring

3) Amniotomy

• thought to cause local release of endogenous PG
• done using amnihook

Complicatons: cord prolapse, Infection, bleeding from vasa praevia, placental separation, failure to induce efficient contractions, amniotic fluid embolism

Question 37

How do we monitor the foetus and mother throughout labour and why is this important?

Answer 37

Partogram

Important to ensure labour is progressing as expected and whether any furthur monitoring is needed

Contains things such as: foetal HR, cervical dilatation, decent of the head compared to hours in labour, number of contractions etc…

Question 38

Some women may require a more continous form of monitoring, what could be used?

What does this detect?

Answer 38

Cardiotocography.

• This monitor detects both the uterine contractions and the foetal HR (two sensors attached to the women, one over foetal heart and other over the uterus)

top reading is foetal HR, bottom reading is uterine contractions

Question 39

What marks the END of the first stage of labour?

Answer 39

When the cervix is 10cm dilated

Question 40

When does the second stage of labour begin and end?

Answer 40

Begins when cervix is 10cm dilated

Ends when foetus has been completly expelled

Question 41

What is the second stage of labour and how long does it usually last?

What do women feel and how does this aid this stage?

Answer 41

Expulsion of the foetus and is relatively rapid, upto 1 hr but can be very fast

Women will feal the urge to ‘bear down’ and push, this along with increasing strength, duration and frequency of contractions facillitate passive movement of foetus down the birth canal

Presenting part appears in birthcanal

Question 42

Explain the steps of foetal passage down the birth canal

Answer 42

1) Head flexes: in oder to reduce diameter of presenting part
2) Head rotates internally: in order for baby to pass through birth canal b/c diameter of inlet is wider than diameter of outlet

• widest part of inlet = transverse position
• widest part of the outlet is in the anterior-posterior position

3) Head stretches vagina and perineum: as it decends towards vulva
4) Crowning: head reaches the vulva and remains visible without slipping back in, head is delivered
5) Head externally rotates and extends: to allow passage of shoulders (external rotation is known as “restitution”)
5) Shoulders rotate: to pass through pelvic outlet, shoulders deliver followed rapidly by the rest

Question 43

During delivery, when the head stretches vagina and perineum what is there a risk of?

Give 2 reasons why and state what can be done to avoid this?

Answer 43

If decent is very rapid or the baby is quite large there is a risk of tearing the perineum.

To prevent this the midwife/obstetrician may decide to may a cut (episiotomy) in the womens perineum in order to help aid delivery of the foetus head

Question 44

Give 4 positions that may be more ideal than sitting that provide comfort to mum (as much as possible) for the best passage of baby

Answer 44

Kneeling, squatting, all fours, water bath

Question 45

Give 6 analgesias that can be used during Labour

Answer 45

1) Oxygen/nitrous oxide (Entonox)

• Inhaled through the mouth by mum
• most effective during peak contractions
• works very quickly but also wears off quite quickly
• can cause nausea

2) Paracetamol
3) Pethidine

• only around 50% effective in labouring women
• may also cause nausea
• takes 15-20 mins to start working (no immediate relief)
• Pethidine is an opioid so there is a risk of respiratory depression in baby if given to close to delivery time (can be easily reversed with naloxone)

4) Pudendal block (given later in labour by anaesthetist)
5) Epidural:
* given by anaesthetist in both first and second stage of labour mix of local anaesthetic + opioids
6) Spinal anaesthesia (given by anaesthetist)

• mix of local anaesthetics + opioids BUT it is injected into spinal fluid (more dense block and longer lasting)
• most commonly used in C-sections

Question 46

Give 4 problems that lead to failure to progress into labour due to “passage”

Answer 46

• abnormal shaped pelvis
• cephalopelvic disproportions
• uterine/cervical fibroids
• cervical stenosis
• circumcision

Question 47

Give 4 problems that lead to failure to progress into labour due to “passenger”

Answer 47

• foetal size
• foetal abnormality
• foetal malpresentaion
• foetal malpostion

Question 48

Give one problem that lead to failure to progress into labour due to “power”

Answer 48

Lack of co-ordinated regular strong uterine contractions

Question 49

Give 2 operative delivery methods when labour does not fully progress

Answer 49

1) Forceps delivery:

• in theatre usually under spinal anaesthetic (incase a C-section is required due to this method failing)
• women is asked to push while they pull using the forceps
• Obstetrician is only allowed a few attempts

2) Vacuum extraction:

• does not have to be done in theatre
• cup is placed on babies head and used in a similar way to forceps to try and extract the baby

These can only be done if they baby is in the appropriate position within the birth canal allowing quick delivery. If the baby hasn’t descended further enough these methods cannot be done and a C-section may be required

Question 50

What are the categories of Cesarean section based on?

What does a C-section that is catagory one mean?

Answer 50

Dependant on the urgency that is needed to deliver the baby (either the wellbeing of the mother or baby) but every category has risks eg. anaesthetics and risk of surgery

Category 1: immediate threat to the life of the mother or baby, highest risk of perinatal mortality/morbidity

Category 2: problems affecting the health of the mother and/or baby but they are not immediately life threatening

Category 3: baby needs to be born early but there is no immediate risk to mother or baby

Category 4: elective surgery operation will be pre-arranged and take place at a suitable time

Question 51

Give 4 reasons why an elective C-section surgery may be arranged (catagory 4)

Answer 51

usually done due to a high risk of problems that could occur during labour

Examples:

• large baby
• if mother is known to have multiple pregnancies
• known pelvic problems/uterus problems such as fibroids
• she has had a C-section previously

Question 52

Briefly explain how a C-section is performed

Answer 52

C-sections are done through an incision in the lower abdomen.

Patient is usually given Spinal anaesthesia

During delivery, head is still delivered first by an obstetrician with assistance who will apply pressure to the top of the uterus

Question 53

When does the third stage of labour begin and end?

Answer 53

Begins with the completed birth of the baby

Ends with the complete expulsion of the placenta and membranes

Question 54

What occurs during the thrid stage of labour and how long does it usually last?

Answer 54

This is complete expulsion of the placenta and membranes

Usually lasts between 5-15 minutes but any period up to 1 hour may be considered within normal limits

Question 55

Explain how the placenta is expelled during the third phase

Answer 55

Following expulsion of the foetus the effect of uterine contractions is dramatically increased

As the uterus contracts down hard the inelastic placenta is squeezed and it shears off. It then ends up being positioned in the lower uterus/upper end of vagina

Around 10mins later the placenta is then expelled completing the third stage of labour

Question 56

Specifically explain how uterine retraction leads to placental separation

Answer 56

In order to seperate the placenta from the uterus:

1) blood in the intra-villus space is forced back into veins of the spongy layer of decidua basilis.
2) the veins become tense and congested and kept under pressure by the underlying muscle layer of the uterus
3) the muscle fibres of the uterus act as living ligature and retract to seal off the blood vessels
4) as a result blood can’t drain back into the maternal bloodstream because the uterus has retracted and doesn’t allow it
5) this causes the blood vessels and blood tracts between the placenta and decidua to ultimately collapse, completing the separation of the placenta
6) It can then be expelled from the body by final contractions

Question 57

How do uterine contractions after expusion of the foetus help reduce the risk of maternal haemorrhage?

How is this iatrogenically enhanced?

Answer 57

They compresses blood vessels in the myometrium

Synthetic oxytocin is administered to the mother directly after expulsion of the foetus. This facilitates the strong contractions to aid removal of the placenta and reduces the risk of maternal haemorrhage

Question 58

What is postpartum haemorrhage?

What are the 2 types

Answer 58

Bleeding form the gential tract of more than 500ml after delivery of the infant

Types:

• Primary: within 24 hrs
• Secondary: between 24 hr and 6w

Question 59

Give 2 stimuli for neonate to take first breath

Answer 59

1) Cold
2) Trauma

Question 60

How does first breath of neonate establish fully function lungs?

Include closure of relevant shunts

Answer 60

As baby takes first breath the resistance in the pulmonary vasculature reduces causing a subsequent increase in the arterial pO2

This leads to a relative increase in pressure within the LA compared to the right resulting in closure of the foramen ovale

As the baby starts to breathe the pO2 within the arterial circulation increases causing the ductus arteriosus to contract/close

Once this happens the foetal circulation is fully converted to that of an adult

Question 61

What 2 shunts must close to establish complete lung function, what are their remnants known as?

Answer 61

1) Foramen Ovale ➞ Fossa Ovalis

⬇pulmonary R = ⬆arterial pO2 = LA pressure > RA = FA closes

2) Ductus Arteriosus ➞ Ligamentum Arteriosum

⬆arterial pO2 = DA contracts/closes

Question 62

How is the newborn assessed immediatly after birth and subsequently following birth?

What are the domains included and what would various scores indicate?

Answer 62

Apgar score: maximum score of 2 per domain, thus total max score of 10

• Activity (muscle tone)
• Pulse
• Grimace (reflex irritability)
• Appearance (skin colour)
• Respiration

Score of 7+: normal healthy baby
Score <7 at immediate birth: requires immediate intervention

Subsequent APGAR scores are performed at intervals after birth in order to ensure they are still well OR if they had a low score before to check intervention is effective and they are showing signs of improvement

Question 63

What is delayed cord clamping?

Give 2 benefits

Answer 63

Delayed cord clamping allows the blood from the placenta to continue being transferred to the baby even after they are born

Benefits include:

• ⬆ iron levels in baby up till 6 months old, helps growth and both physical and emotional development
• ⬆ amount of stem cells, helps growth and immune system