10.1 Labour And Delivery Flashcards
What is labour?
The expulsion of the products of contraception (placenta and fetus) after 24 weeks of gestation.
What is parturition?
Spontaneous abortion. Expulsion of the products of pregnancy (fetus and placenta ) before 24 weeks of gestation.
What is pre-term labour?
Labour that occurs before 37th week of gestation. Also known as premature labour
What are the 5 steps required form expulsion of the fetus?
- 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
- Expulsion of the fetus
- Expulsion of the placenta and changes to minimise blood loss from the mother
What rocesses occur in the first stages of labour
Creation of the birth canal
Release of the structures which normally retain the fetus in utero
When does the uterus become palpable?
At 12 weeks
Where has the uterus grown to by 20 weeks?
Levels of the umbilicus
Where has the uterus grown to by 36 weeks?
Up to the level of the xiphisternum
How does the fetus normally lie?
The commonest lie is longitudinal, with the head or buttocks posterior. The fetus normally has a flexed attitude.
What does lie of the fetus mean?
This describes the relationship of the long axis of the fetus to the long axis of the uterus
What does the presentation of the fetus describe?
This describes which part of the fetus is adjacent to the pelvic inlet
What is breech presentation?
When the baby is lying longitudinally and the presenting part is the podalic side.
What is vertex presentation?
Longitudinal lie with the head lying inferiorly/ presenting.
What is shoulder presentation?
What the fetus lies in the horizontal plane.
What does the clinical management of labour depend on?
lie, presentation and position of the fetus
In common presentation, when fetus lies longitudinally in a vertex presentation and well flexed, what is the diamater of presentation?
9.5 cm
Ordinarily, how wide must the birth cancel be?
10cm
What determines the limits of the birth canal diameter?
The pelvis
What is the boundaries of the pelvic inlet?
- 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.
What is the normal true diameter of the pelvic inlet?
11cm
How might there be expansion of the pelvic inlet from the normal true diameter?
Softening of the pelvic ligaments
How is the fetus maintained in the uterus?
cervix and relative inactivity of the myometrium
How does the cervix create the brith canal?
Dilate
Retract anteriorly
What causes cervical dilation?
Cervical ripening = Structural changes facilitating cervical dilation.
Produced by forceful contractions of uterine smooth muscle.
What is effacement?
The thinking of the cervix before dilation
What are the microscopic structural changes occurring during cervical ripening?
- Marked reduction in collagen content of cervical connective tissue , marked increase in glycosaminoglycans (GAGs). Decreased aggregation of collagen fibres mean collagen bundles ‘loosen’
- Influx of inflammatory cells, and increase in nitric oxide output.
What happens when ‘waters break’?
Fetal membrane rupture releasing amniotic fluid
What triggers cervical ripening?
prostaglandins, namely E2 and F2α.
What forms the myometrium?
Bundles of smooth muscle cells
How does the myometrium get thicker in pregnancy?
Increased smooth muscle cell size.
Glycogen deposition
How is a contractive force generated by the myometrium?
Myometrum = smooth muscle
- Action potentials in cell membrane spread from cell to cell via specialised gap junctions.
- trigger rise in intracellular calcium
- Calcium ions bind to calmodulin to form calmodulin-Calcium complex
- Calmodulin:calcium complex binds to inactive myosin light chain kinase to form active myosin light chain kinase.
- Active myosin light chain kinase phosphorylates the myosin light chain enabling crossbridge to actin filament
- Contraction initiated
Why is the myometrium described as spontaneously motile?
As some of the smooth muscle cells are capable of spontaneous depolarisation and action potential generation. Can act as pacemakers
What are Brixton-hicks contractions?
Infrequent contractions of higher amplitude that occur before delivery
What 2 hormones influence change in the frequency and force of contractions of the myometrium during labour?
- Prostaglandins - enhance release of calcium from intracellular stores
- Oxytocin - peptide hormone released from the posterior pituitary under control of neurones from the hypothalamus. Lowers threshold for triggering action potentials.
What is cervical effacement?
Borrowing / thinning of the cervix during the onset of labour.
What is the action of the Ferguson reflex?
Positive feedback loop that acts to increase oxytocin secretion from the posterior pituitary gland to increase contractions.
Describe the Ferguson reflex
Sensory receptors in the cervix and vagina are stimulated by contractions; excitation passes via afferent nerves to the hypothalamus, promoting massive oxytocin release. This ‘positive feedback’ makes contractions more forceful and frequent.
What is brachystasis?
A property of uterine smooth muscle. During contractions, uterine smooth muscle shortens but then don’t fully relax afterwards. This allows the fundal region of the uterus to progressively shorten.
What is the purpose of brachystasis?
To push the presenting part of the fetus into the birth canal and stretch the cervix over it
How is labour initiated in animals ?
Rising production of cortisol by the fetus
Initiates fall in progesterone levels relative to oestrogen.
This decrease in progesterone stimulates increase in prostaglandin and oxytocin secretion
Where are oestrogen and progesterone produced in pregnancy?
The placenta
What can be given medically to induce labour?
Prostaglandins
Why might fetal heart rate decrease during labour?
Increasingly forceful uterine contractions may temporarily reduce placental blood flow, and so reduce oxygen supply to the fetus. Fetal heart rate decreases in response to hypoxema
When does the first stage of labour end?
When dilation of the cervix reaches 10cm
How long does the second stage of labour last?
Multiparous woman: up to an hour
Primigravida : up to 2 hours
What are the stages of the second stage of labour?
- The descended head flexes as it meets the pelvic floor, reducing the diameter of presentation.
- There is then internal rotation.
- The sharply flexed head descends to the vulva, so stretching the vagina and perineum.
- The head is then delivered (‘crowning’), and as it emerges it
rotates back to its original position and extends. - The shoulders then rotate followed by the head, and the
shoulders deliver, followed rapidly by the rest of the fetus.
How does the second stage of labour end?
With the delivery of the fetus
If the fetal shoulder does not deliver without medical intervention, what condition can occur?
Shoulder dystocia
What occurs in the third stage of labour?
- Powerful uterine contractions
- Placenta separated from the uterus and positioned in the upper part of the vagina or lower uterine segment
- placenta and membrane normally expelled within 10 minutes
What is the purpose of uterine contractions after completion of the second stage of labour?
- To separate and expel the placenta and membranes
2. To compress the blood vessel and reduced bleeding
How can contractions of the uterus be enhanced?
By administering oxytocic blood
What triggers the baby to take its first breath?
Delivery trauma
Temperature change
How does the firsts breath of the fetus influence the relative pressures of the atria?
- First breath causes a fall in pulmonary vascular resistance.
- Reduction in pulmonary arterial pressure
- Increase in pulmonary venous pressure
- Increase in left atrial pressure relative to right atrial pressure
Why does the foramen ovale shut after fetus takes first breath?
First breath triggers the left atrial pressure to increase relative to the right atrial pressure.
Changes direction of flow between the atria at the foramen ovale.
Septum primeur pushed against the septum secundum, closing the foramen ovale.
Inhalation after birth causes rise in pO2 of fetal blood. Why is this significant to the development of the CVS of the newborn?
Rising arterial pO2 causes the ductus arteriosus to constrict and close. This stops the connection between the pulmonary trunk and the aortic arch.
Sphincter in the ductus venosus constricts, so all blood entering the liver passes through the hepatic sinusoids.
How is the condition of the neonate assessed following delivery?
Assessed using the APGAR score. Assessed twice, firstly after delivery and then 5 minutes after.
Generates a score from 1 to 10: the higher the number the healthier the baby
What is assessed in the APGAR score?
Appearance Pulse Grimace Activity Respiration
What are the elements of pregnancy classified into?
The powers, the passage and the passenger
What are the elements of the powers?
Contractions of the myometrium which are assessed in terms of frequency, amplitude and duration.
Brachystasis causing shortening of the cervix and fundus of the uterus
What elements of labour are considered in the passage?
The passage refers to the birth canal which is formed by the bony pelvis and soft tissues.
The fetus flexes, extends and rotates as it passes through the birth canal. Resistance of the soft tissue can slow labour.
What elements of labour are considered in the passenger?
Size and presentation of the fetus.
The orientation of the head in cephalic delivery can vary and as such the head diameter of the fetus varies in different positions.
How might fetal anatomy change during delivery?
Shape of fetal skull may vary. Moulding of the fetal cranium may occur since cranial sutures have not yet fused. Often results in caput swelling
What may cause failure to progress in labour?
Inadequate power (insufficient uterine contractions) Inadequate passage (abnormal bony pelvis, rigid peritoneum) Abnormalities of the passenger ( fetus too big, fetal presentation)
How is progress in labour graphed?
Plotted graphically on a partogram
What neurological structure is damaged during shoulder dystocia?
Brachial plexus (usually C5 to C7)
What is ebs palsy?
Also known as waiters tip.
Damage to the C5-C7 spinal cords during shoulder dystocia. Presents as medial rotation at the shoulder, extension at elbow, flexion at wrist, pronation and weakness of affect arm.
What is the difference between a normal birth and a normal delivery?
Fetus expelled through vaginal canal in both
In normal delivery medical assistance is provided
In normal birth the mother births the baby on her own with no assistance
How does the uterus usually lie in the pelvic cavity?
Lies anteverted and antiflexed
What are the normal non-pregnant measurements of the uterus?
Length = 7.5cm Width = 5cm Depth = 2.5cm
What are the 3 layers of the uterus?
Inner myometrium
Transitional layer
Outer, thin sheet of smooth muscle containing elastin
What are the 3 different types of muscle fibres in the myometrium?
Longitudinal muscles - symphysis pubis over the fundus back down
Circular muscles - at the cornua and cervical region
Oblique muscles - across the uterus
What is term?
37 to 42 weeks of pregnancy. When normal labour occurs
How long does normal labour last?
Primiparous women – 8 to 18hrs
Multiparous women– 5 to 12 hrs
When does the first stage of labour start?
When there is increased regular contractions of at least 2 contractions every 10 minutes. Contractions painful enough that mother stops talking.
How can the first stage of labour be divided?
Latent phase = up to 4cm dilation of the cervix
Active phase = from 4cm to 10cm dilation of the cervix
During the active phase of the 1st stage of labour, how quickly should dilation be occurring?
Half a cm to a cm an hour
What is lightening?
Occurs 2-3 weeks prior to the onset on labour. When the fundal height reduces.
What occurs in lightening?
- Expansion of the lower segment
- Fetal head engages (presenting part enters pelvis)
- Symphysis pubis widens, sacro-iliac joints relax
- Pelvic floor relaxes
- Increased vaginal secretions
- Frequency of micturition
- Braxton Hicks contractions
- Taking up of the cervix
What is the theory of mechanical initiation of labour?
Uterus grows and stretches, detected by stretch receptors in the wall of the uterus, critical degree of stretch, contractions
Contractions are caused by stimulation of the cervix – pressure from presenting part
Describe the theory of hormonal initiation of labour?
Level of progesterone decrease and oestrogen levels rise.
Stimulates production of prostaglandins from placenta, decidua and membranes
Stimulates oxytocin release from posterior pituitary
Describe the theory of prostaglandin initiation of labour
Reduction of prostaglandins inhibiting substances prior to term
Increase prostaglandin release during the onset of labour facilitates liberation of calcium ions from intracellular stores in myometrium – increases cell contractile activity
In cervix facilitates production of enzymes (collagenases) -> reduces collagen by digestion -> glycoaminolcans -> increases cervical ripening
How is oestrogen thought to help initiate labour?
Oestrogen levels increase in the last few weeks Oestrogen thought to stimulate:
• An increase in oxytocic receptors in myometrium
• An increase in gap junctions in myometrium
• Placenta to release prostaglandins leading to production of collagenases –digest collagen in cervix-help to soften
Balance between oestrogen and progesterone facilitates myometrial activity
Describe what is meant by the fetal theory of initiation of labour
Onset due to ACTH from fetal pituitary leading to:
1. Increase in fetal cortisol from the fetal adrenal glands. Converts progesterone to oestrogen. Increases uterine sensitivity to prostaglandins and oxytocin Stimulates release of prostaglandins from placenta and myometrium
2. High concentrations of oxytocin found in umbilical circulation. Thought to arise from the fetus and transferred to maternal circulation to induce labour.
However fetal death/ brain /adrenal malformation does not prevent labour
Describe the theory of nitric oxide initiation of labour?
Placenta produces nitric oxide
Nitric Oxide maintains relaxation of uterus during pregnancy
Reduction of Nitric Oxide at term increases the excitability of the uterus.
What hormones are involved in labour?
Progesterone Oestrogen Prostaglandins Oxytocin Endorphins Adrenaline/ Noradrenaline
What are the contributing factors to expulsion of the fetus?
Intrauterine hydrostatic pressure
Pacemaker in the fundus
Fundal dominance, longitudinal muscles contracting
Resting tone, allowing myometrium to become reoxygenation
Brachystasis
Formation of forewaters and hindwaters - general fluid pressure
Fetal axis pressure - Flexion of fetus head
Effacement
Retraction – Bandls ring
Dilatation
Show - plug of mucus in cervix releases
What is meant by fundal dominance?
Fundal dominance – contractions begin at the cornua and remain strongest at this point. They spread out and down towards the lower segment in waves.
How does effacement in a multigravida vary from a primagravida?
Primagravida = effacement occurs before dilatation Multigravida = effacement and dilatation occurs at the same time
What is show?
As the cervix dilates the plug of mucus (Operculum) comes away.
This may be streaked with blood.
Not always indicative of the imminent onset of labour
What affects does labour have on the mothers physiology?
Rise in CO
Increased BP and Pulse
Haemoconcentration and hypercoagulation
Tingling fingers and toes, dizziness (alkalosis due to hyperventilation)
Maternal acidosis
Delayed gastric emptying and motility
Altered renal output ( increased renin and angiotensin)
Why is it highly important that all of the placenta and membranes are removed during the third stage of labour?
As placenta secretes progesterone and oestrogen. These hormones will prevent woman from effectively lactating.
