Parturition Flashcards
Outline the hormonal changes that occur around parturition
- Drop in progesterone, increase in oestradiol
- Increase in foetal cortisol
- Increase in prolactin
How does cortisol affect the oestrogen:progesterone ratio?
- Rise in foetal cortisol increases oestrogen:progesterone ratio
- Upregulates aromatase enzymes
- Convert androgens to oestrogens
- Reduces progesterone production
What are the potential endocrine reasons for delayed parturition?
- Too much progesterone
- Too little oestradiol preventing increased oxytocin
- Decreased glucocorticoids
What is the dominant hormone during pregnancy?
Progesteron
What is the major hormonal change that occurs prior to parurition?
Switch from progesterone to oestrogen
What happens to foetal cortisol approaching parturition?
Cortisol increases (is the stimulus for parturition)
What initiates parturition?
Foetal cortisol levels
What causes the increase in foetal cortisol?
- Increased stress of foetus
- In response to reachign maximal size within available space and reaching maximal nutritional demands
How does foetal cortisol cause changes that will ultimately lead to parturition?
- alters catalytic enzymes
- Progesterone converted to oestradiol using series of enzymes, upregulated by foetal cortisol
- Also stimulates productin of surfactant in lungs
What are some functions of glucocorticoids?
- Affect glucose metabolism (inhibit insulin)
- Anti-inflammatory and immuno-suppressive
- Negative feedback to hypothalamus and ant. pit in HPA axis
- Increases uterine secretions
- Stimulates uterine prostaglandin production
What changes allow myometrial contractions to take place?
- Increase in foetal cortisol
- Decrease in progesterone to remove block
What may cause prolonged gestation?
- Lack of HPA axis
- Inability to produce foetal cortisol
- e.g. ingestion of “skunk cabbage” producing cyclopic lamb with absence of hypophysial stalk and pituitary, and adrenal hypoplasia
Explain the importance of uterine prostaglandin production prior to parturition
- Stimulated by foetal cortisol
- Causes uterine contraction
- Acts on ovary and causes lysis of CL to further reduce progesterone levels
- Stimulates relaxin production
What is the role of relaxin in parturition?
Increases elasticity of cervix for parturition
What stimulates oxytocin release during parturition?
- Pressure from the foetus on the cervix
- Controlled by neurohormonal reflex
Describe the neurohormonal reflex in oxytocin release
- Increasing pressure on cervix stimulates pressure sensitive neurons
- Relay afferent info to PVN of hypothalamus
- Neural input to posterior pituitary = oxytocin release
- Induces further contractions, increases pressure, positive feedback loop
Outline the use of glucocorticoids for induction of parturition
- Induce abortion/parturition in late term gestation
- Support final developmental stages of young in humans (surfactant)
- Mimic action of foetal cortisol
Outline the use of oxytocin in the induction of parturition
- Given to strengthen contractions and expel placenta/membranes
- e.g. uterine inertia, removal of uterine produced, retained placenta
Outline the use of PGF2a in the induction of parturition
- Causes luteolysis
- Strengthens contractions
- Give prior to/during delivery
Outline the use of beta-adrenergic agonists in parturition
- Inhibits contractions and causes relaxation
- Given to reduce contractions e.g. in C-section, or to correct dystocia
Outline the actions of the mediators of contraction
- Stretch increases COX-2 and oxytocin receptors
- Oxytocin binds to receptors to simulate contraction (positive feeback) and also increases arachidonic acid
- Arachidonic acid converted by COX-2 to PGE and PGF2a
- PGs potentiate oxytocin
- Oestradiol increases COX-2 and oxytocin receptors
Describe the biochemical mechanisms in myometrial contraction
- Hormone (oxytocin) binds to membrane receptor
- Second messenger signalling
- Calcium into cytoplasm from SER or extracellular sources
- Calcium binds to calmodulin forming complex
- Complex interacts with MLCK, needed for myosin activation (phosphorylates myosin)
- Myosin binds to actin, walks up to generate pull
- Contraction in all planes due to fibres running in multiple
directions - No troponin complex for regulating contraction
Describe the physical contraction mechanism in myometrium
- 3D as fibres run in different directions
- Actin fibres attach to cell wall and dense bodies in cytoplasm
- When activated, slide over myosin bundles causing shortenin go f cell walles
- No striations
- Myosin performs powestroke
Describe the role of gap junctions in the coordination of contractility
- Low resistance pathways allowing action as functional syncitium
- Allow passage of small molecules
- Increase in number and size towards parturition
- Oestradiol stimulates their production
- Presence and permeability under steroid and PG control
- Some influence of stretch
Describe the structure of gap junctions in the myometrial myocytes
- Made up of connexons and connexins, half in each cell
- Each connexon is made up of 6 connexins
What is the role of progesterone in myometrial activity?
Inhibits it
What is the role of oxytocin in myometrial activity?
- Stimulates cascade of events leading to contraction
- Increases force, duration and frequency of contractions
What is the role of oestradiol in myometrial activity?
- Stimulates production of gap junctions
- Makes contractions more likely
- Allows synchornous contraction
What is the role of prostaglandins in myometrial activity?
- Isoform locally produced to act locally
- PGF2a = contraction
- PGI2 = relaxation
- PGE2 = cervical softening
What is the neural input into myometrial activity?
- Autonomic via pelvix plexus innervates uterus through alpha1 and 2 and beta 1 and 2 adrenergic receptors
- Alpha-1 activation causes contraction
- Beta-2 activation causes relaxation
- High progesterone increases number of beta receptors
What are the stages of parturition?
- INitiation of myometrial contractions
- Expulsion of the foetus
- Expulsion of the foetal membranes
Describe the first stage of parturition
- Onset of uterine contractions
- Foetus produces cortisol, upregulation of enzymes
- P4 to E2
- Removal of P4 block on contractions
- Increased E2 increases repro tract secreions
- Cortisol increases uterine PGs
- PG causes relaxin prod
- Degradation of collagen and remodelling of cervical matrix over period of hours to days
- Cervical os opens
- PG lyses CL if present
- Uterine contraction increases due to increase in PGF2a and E2
- Foetus assumes disposition for expulsion
Outline the onset of coordinated myometrial contractions
- Transition from uncoordinate to regular peristaltic type
- Duration, frequency and amplitude increase
- Peristaltic waves towards vulva
Describe assumption of foetal disposition for parturition in general
- Adoopts characteristic position for passage through cervix to vagina then vulva
- Some species variation
- Trigger for foetal response unknown *may be result of increasing uterine pressure
Describe assumption of foetal disposition in foal and pup
- Rotation from ventral to dorsal position
- Forelimbs, head and neck extend
Describe assumption of foetal disposition in calf and lamb
Simple extension of limbs and head
Describe the reduction in attachment of placenta in teh first stage of parturition
- Uterine contractions cause less intimate attachment
- Superficial cells undergo fatty degeneration
- in species with deciduate placenta, separation of margins and haemorrhage begins
Give the signs of the first stage of parturition
- Uterine/myometrial contractions
- Anorexia, shivering
- Nesting behaviour
- Vulval discharge
Compare the second stage of parturition in monotocous and polytocous species
- Monotocous: one foetus to be delivered, expulsion of foetus
- Polytocous: multiple foetuses to be delivered, cannot spearate second and third stage
Describe the second stage of parturition
- Expulsion of foetus
- Onset of abdominal contractions
- Ferguson’s reflex initiated
- Allantochorion ruptures as consequence of movements towards teh cervix
- Contractions continue, amnion at vulva
- Foetal limbs in amnion
- Foetus hypoxic in birth canal
- Foetal head at vulva, maximal contractile effort
- Complete when all foetuses delivered
Describe Ferguson’s reflex
- Does not involve abdominal contractions
- Caused by force of foetus against cervix
- Neurohormonal refelx to release more oxytocin which in turn increases contractions, more pressure so more stimulation of PVN and more oxytocin etc
What is the significance of the foetus being hypoxic in the birth canal?
- Promotes foetal movement
- Stimulates more myometrial contractions
When do the abdominal contractions take place in stage 2 of parturition?
- Short window, mostly myometrial contractions
- High impact in specific stages
- Superimposed on beginning of specific myometrial contractions to increase uterine pressure
What is the stimulus to breathing following parturition?
Air on nostrils
Describe the third stage of parturition
- Expulsion of placenta
- After foetal expulsion, regular abdominal contractions cease
- Myometrial contractions more frequent but less strong and less regular
- Vasoconstriction of arteries supplying chorionic villi
- Maternal vasoconstriction where there is haemochorial placenta
- Uterine contractions open endometrial crups and allow separation of foetal membrane
Describe the importance of the change in myometrial contractions in the third stage of parturition
- Important for dehiscence and expulsion of foetal memrbanes
- Dehiscence is separation of foetal memrbanes
Describe the myometrial contractions in the third stage of parturition
- Decreased amplitude, more frequent, less regular
- Waves from uterine tube to cervix
- Opposite direction in cow and sow to aid dehiscence
Describe the consequence of vasoconstriction of the arteries supplying the chorionic villi
- Villi decrease in size
- Released from crypts
- Caruncle decreases in size
Describe the eversionof the placenta in the mare
- Foetus breaks through amnion at cervical star (little/no attachment/villi here)
- Amnion breaks
- Allantochorion follows by rolling away from wall, starting at tip of gravid horn usually
- Form mass within pelvis, stimulates abdominal contractions
- Expulsed inside out
What occurs during the puerperium?
- Reproductive tract reduces in size to similar to before pregnancy
- Between 2-8 weeks depending on species
- Often have mucoid vulval discharge
What terms are used to describe disposition of the foetus?
- Presentation
- Position
- Posture
Define foetal disposition
The spatial arrangement of the foetus in relation to the pelvis and birth canal of the dam and of its extremitites to itself. Describe as normal or abnormal.
Describe what is meant by foetal presentation
- Relation between longitudinal axis of foetus and maternal birth canal
- Can be longitudinal or transverse
- Can be cranial or caudal, dorsal or ventral
What is meant by cranial longitudinal foetal presentation?
Head first, spine to spine
What is meant by caudal longitudinal foetal presentation?
Tail first, spine to spine
What is meant by dorsal transverse foetal position?
On its side, spine of foetus towards birth canal
What is meant by ventral transverse foetal presentation?
On its side, ventrum of foetus towards birth canal
Describe what is meant by foetal position
- indicates surface (quadrant) of maternal birth canal, to which the vertbral column of the foetus is apposed to
- Dorsal, ventral, left lateral, right lateral
What is meant by dorsal foetal position?
Spine of foetus to top of birth canal
What is meant by ventral foetal position?
Spine of foetus to bottom of birth canal
What is meant by left lateral foetal position?
Spine of foetus in contact with left wall of birth canal
What is meant by right lateral foetal position?
Spine of foetus in contact with right wall of birth canal
Describe what is meant by foetal posture
- The disposition of the moveable appendages ofthe foetus
- Involves flexion or extension of the neck and joints
- Flexion of neck describe with direction e.g. laterally and to the right
- Flexion of limbs identified as which joint e.g. hip, shoulder etc and which limb
What are the normal dispositions?
- Cranial longitudinal presentation, dorsal posture, extension of neck and forelimbs
- Caudal longitudinal presentation, dorsal position and extension of hindlimbs
What is meant by breech?
Caudal longitudinal presentation, dorsal position adn hindlimbs flexed at hips
What is meant by dystocia?
Difficulty in birth, does not always relate to abnormal disposition
What factors influence the incidence of dystocia?
- Varies by species
- Breed
- Age
- Parity
- Body conditin
- Environment
Give some common causes/features of dystocia
- Foetus (or part of it) too big/dam too small
- Abnormal disposition
- Multiple foetuses
- Poor or absent uterine contractions (primary or secondary inertia)
Compare primary and secondary uterine inertia
- Primary: lack of contraction from teh beginning
- Secondary: myometrium becomes exhausted e.g. after multiple foetuses
Give common causes of dystocia in the cow
- Foeto-maternal disporportion
- Foetal disposition
- Complete vagina/cervical dilatation
- Uterine inertia
- Uterine torsion
- Cervical prolapse
- Foetal monsters/abnormalities
What is traction when relating to parturition?
- The application of force to presenting parts of the foetus in order to supplement or replace the maternal forces
- In most cases of moderate foeto-maternal disporportion will be sufficiently treated by application of traction
What are the risks involved in using traction to aid parturition?
Excesive force applied inappropriate may cause severe trauma to dam and foetus
What should an investigation of possible dystocia include?
- Clinical history
- General examination
- Obstetrical examination
- Formation of conclusion
What are important points to cover in a case history for a dystocia case?
- Premature/overdue
- Parity
- Sire information
- Recent observations of dam
- Vulval discharge
- Uterine/abdominal contractions
- Foetal membranes/fluid
- Any foetuses delivered
- Need to establish what stage of parturition
What are important points to cover in a general examination in a dystocia case?
- Bright/dull
- Body condition
- Ability to stand/walk
- Clinical parameters
- Presence of foetal parts at vulva
- Vulval discharge
- Abdominal distension
- evidence of foetal life
- Clinical condition determines steps taken
How can foetal life be established prior to parturition?
- Apex beat of heart
- Suck reflex
- Limb pulses
- Response when stimulate anus
- Withdrawal reflex etc
What are the important points to cover in an obstetrical examination when dealing with a dystocia case?
- Vaginal examination
- Vestibule dilation
- Vaginal dilation
- Cervical dilation
- State of lubrication of tract
- Foetal presence and life, and disposition
- Foetal membranes present and intact?
- Relative size of birth canal and likelihood of foetuses beign delivered
- Lacerations
What is important to ensure following delivery in a dystocia case?
- No other foetuses
- No lacerations/perforations
- No obvious other defects e.g. pelvic fractures, mastitis etc
What is the most common cause of dystocia in cows?
Oversize
What is the most common cause of dystocia in dogs and cats?
Primary uterine inertia
What are the general principles of management of a dystocia case?
- Establish treatment plan
- Conservative treatment (minimal intervention where possible)
- Manipulative treatment
- Drug therapy
- Surgical treatment
- Euthanasia
Discuss teh general principles of manipulative treatment of a dystocia case
- Drugs needed (tocolytic, epidural)
- Oxygen to foetus where possible
- Lubrication
- Anchoring devices to identifiable structure
- Mutation for correcting presentation, position or posture
What tools can be used for traction of the foetus?
Ropes and snares, chains in some cases, vectis forceps
When is traction best applied?
Best time to apply traction with contractions, and maintain in between to prevent reverse movement of foetus
What tools can be used to apply traction when the foetus is dead?
Variety of hooks e.g. eye hooks, General and self-closing hooks
When applying traction, why might slight rotation of the foetus be advantagious
- Largest diameter of birth canal if 5-past-7 or 5-t-5 position
What do you need to consider when delivering a foetus, with regards to the umbilicus?
- When umbilicus pressed against pubis, blood supply to foetus compromised
- Especially in posterior presentation
In what direction should traction be applied?
Downwards
What is a fetotomy?
- Removal of parts of the foetus where the feotus is too large to come as one part or cannot be removed in another way
- Only when foetus dead
Compare percutaneous and subcutaneous foetotomry
- Percutaneous: used in calves, cuts through skin using wire
- Subcutaneous: foetotomy knife, cut skin and remove from lamb to remove limb
What are the 6 major indications for carrying out a Caesarean section in the cow
- Inadequate cervical dilatation
- Uterine torsion that cannot be rectified
- Foetal deformity (e.g. schistosoma reflexus)
- Narrow undersized pelvis of mother
- Abnormal pelvic conformation
- malpresentation of foetus that cannot be corrected
Outline the principles of a C-section in the cow
- In through left, rumen blocks intestines from falling out
- When puncture peritoneum will hear rush of air
List complications that may arise from a C-section in the cow
- Punctured rumen
- Continued straining during procedure which may push rumen out and creates moving target
- Lying down during procedure
- Disagreement in what a successful outcome is
What things may help reduce challenge associated with bovine abdominal surgery on a farm?
- Fix cow’s head
- Push cow with RHS against wall/barrier
- Gate along front half of LHS
- Crush with cow half in half out
- Plenty of clean straw
- Good lighting
- Rope over withers to prevent kicking
- Sedation may be necessary
For the bitch, give the
a. duration of 1st stage of parturition
b. duration of 2nd stage
c. duration of 3rd stage
d. time from delivery to offspring mobility
e. time from delivery to suckling
a. 6-12 hours
b. 6 (24 h in large litters)
c. most placentas pass with neonate or within 15 mins of birth
d. 30-60 min
e. 30-60 min
For the queen, give the
a. duration of 1st stage of parturition
b. duration of 2nd stage
c. duration of 3rd stage
d. time from delivery to offspring mobility
e. time from delivery to suckling
a. 1-2h for 1st kitten
b. can pause fo 12-24h
c. membranes soon after each kitten
d. 30-60min
e. 30-60min
For the mare, give the
a. duration of 1st stage of parturition
b. duration of 2nd stage
c. duration of 3rd stage
d. time from delivery to offspring mobility
e. time from delivery to suckling
a. 1-4h
b. 12-30min
c. 1h
d. 10-30min
e. 60-120 min
For the cow, give the
a. duration of 1st stage of parturition
b. duration of 2nd stage
c. duration of 3rd stage
d. time from delivery to offspring mobility
e. time from delivery to suckling
a. 6-12h
b. 0.5-4h
c. 4-12h
d. 20-40min
e. 2-4h
For the sow, give the
a. duration of 1st stage of parturition
b. duration of 2nd stage
c. duration of 3rd stage
d. time from delivery to offspring mobility
e. time from delivery to suckling
a. 2-12h
b. 150-180miin
c. each set passed with next piglet from that horn
d. 10-20min
e. 15-30min
For the ewe, give the
a. duration of 1st stage of parturition
b. duration of 2nd stage
c. duration of 3rd stage
d. time from delivery to offspring mobility
e. time from delivery to suckling
a. 2-6h
b. 0.5-2h
c. 0.5-8h
d. 10-20min
e. 30-60min
