3. parturition and dystocia Flashcards
what are the stages of parturition
- stage of preparation
- first stage parturition (initiation of contractions)
- second stage parturition (expulsion of fetus)
- third stage parturition (expulsion of placenta)
- puerperium
what happens during the preparation stage of parturition
- prep for imminent parturition
- production of the polypeptide hormone relaxin
- causes relaxation of the pubic symphysis, vulval and perineal tissues
where is relaxin produced in preparation for parturition in the cow, horse, dog, cat
horse, dog, cat: by the placenta
cow: by the CL
what occurs during the first stage of parturition
- fetal cortisol increases
- enzymes convert progesterone to oestradiol
- progesterone declines removing the block on mymetrial contractions
- increased basal uterine contractions
- elevated oestrogen increases reproductive tract secretions (esp from cervix
- uterine prostaglandin increases
- lysis of CL if present
- uterine contraction due to increase in pgf2a and oestrogen
- further relaxin produced causing changes to cervix
- degradation of collagen and remodelling of cervical matrix over period of hours to days
- cervical os opens
- onset of coordination of myometrial contractions (trnsition from uncoordinated to regular peristaltic type, duration, frequency and amplitude increases)
- fetus assumes the disposition for expulsion
- uterine contractions cause the placental attachments to the endometrium to become less intimate (superifical cells undergo fatty degeneration, in deciduate placentas separation of margins and hemorrhage occurs)
discuss fetal disposition in preparation for parturition in different species
- in foal and pup there is rotation from ventral to dorsal position and the forelimbs, head and neck extend
- in calf and lamb there is simple extension of the limbs and head
- trigger is unknown but may be result of increasing uterine pressure
list signs of first stage parturition
- uterine (not abdominal) contractions
- anorexia
- shivering
- nesting behaviour
- vulval discharge
what occurs during the second stage of parturition
- monotocous sp: expulsion of fetus
- polytocous sp: cannot separate second and third stage
- first sign is onset of abdominal contractions superimposed upon beginning of uterine contractions (increase uterine pressure)
- fergusons reflex (neuro-hormonal reflex -> brain release oxytocin -> myometrial contraction)
- abdominal contractions are not related to release of oxytocin
- allantochorion ruptures as a consequence of its movement towards the cervix (allantoic escapes vulva and acts as lubricant)
- contractions continue, amnion appears at vulva
- fetal limbs appear in the amnion; in monotocous sp one limb precedes the other
- amnion may or may not be ruptured
- as fetus enters birth canal it becomes hypoxic promoting fetal movement which further stimulates myometrial contractions
- the fetal head reaches the vulva and the contractions of the uterine and abdominal muscles reach a climx of expulsive effort
- air at nostrils of fetus stimulates breathing
- if given birth in lateral recumbency, umbilical cord might not rupture as requires gravity but will rupture on own (allow to happen to allow transfer of blood to fetus)
- when rupture occurs, two umbilical arteries and urachus retract into the abdomen and this prevents hemorrhage
- complete when all fetuses delivered
what is the fergusons reflex
how long is second stage parturition meant to last across species
cow: 1 hour
ewe: 1 hour
sow: 3 hours
mare: 30 minutes
bitch: 6 hours
queen: 2 hours
what are normal presentations of delivery in the mare, cow and ewe
cranial dorsal and extended
also caudal dorsal extended ok, NOT breech
what occurs during the third stage of parturition
- after fetal expulsion regular abdominal contractions largely cease
- myometrial contractions decrease in amplitude but become more frequent and less regular to expel the membranes (both directions)
- lack of fetus results in vasoconstriction of the arteries supplying the chorionic villi
- villi decrease in size and are released from crypts
- where there is haemochorial placental there is maternal vasoconstriction that reduces hemorrhage
- uterine contractions cause opening of endometrial crypts, exsanguination of the placenta and separation of fetal membrane
- as a result, in diffuse placentae the apex of the allantochorionic sac becomes inverted and the sac is rolled fown the uterine horns
- when a large portion of the inverted membranes form a mass within the pelvis it stimulates reflex abdominal contractions
- the allantochorion is expulsed with its smooth, shining allantoic surface outermost
- in polytocous species the expulsion is intersersed between fetal births
- can last between 1 hour (mare) and 6 hours (cow)
what happens during the puerperium
reproductive tract reduces in size to similar that before pregnancy
- 2-8 weks depending on species
- often see mucoid vulval discharge
fetal presentation refers to
the relation between the longitudinal axis of the fetus and the maternal birth canal
- longitudinal or transverse
fetal position refers to
indicates the surface of the maternal birth canal to which the vertebral column of the fetus is apposed
- dorsal, ventral, left or right lateral
what is meant by fetal posture
refers to the disposition of the moveable appendages of the fetus and involves flexion or extension of the neck and limb joints
describe the disposition of this fetus
cranial longitudinal presentation, dorsal position, extended posture
is this normal disposition of the fetus and what is it called
yes
caudal longitudinal presentation, dorsal position, extended posture
what are the common features/ causes of dystocia
- fetus (or part of it) too big or dam too small
- abnotmal fetal disposition
- multiple fetuses
- poor or absent uterine contractions (primary or secondary inertia)
what are the most common causes of dystocia in cows
