Lecture 13: Parturition - Normal birth Flashcards
What are the three P’s of labour?
- Passage
- Power
- Passenger
Challenges in Human Parturition?
- Quiescence: of uterus with growth, distension. pressure (fetus + amniotic fluid)
- Timing: for safe birth
- Activation: stimulation of uterine musculature changes in genital tract
- Birth: fetal-neonatal adaptations (sudden loss of placental life-line)
- Involution: homeostasis, establishing lactation
What is the principle hormone to maintain quiescence?
Progesterone, produced from the corpus luteum (and placenta).
Although a multitude of hormones are required for this, it take more then >1 to be abnormal/removed before quiescence can be undone
What affects Gestation Length?
- Parity (if you’ve had kids before GL: shorter)
- Age: older you are GL: shorter
- Genetics (maternal and paternal)
- Race/ethnicity
Challenges in Human Parturition?
- Quiescence: of uterus with growth, distension. pressure (fetus + amniotic fluid)
- Timing: for safe birth
- Activation: stimulation of uterine musculature changes in genital tract
- Birth: fetal-neonatal adaptations (sudden loss of placental life-line)
- Involution: homeostasis, establishing lactation
What is the principle hormone to maintain quiescence?
Progesterone, produced from the corpus luteum (and placenta).
Although a multitude of hormones are required for this, it take more then >1 to be abnormal/removed before quiescence can be undone
What affects Gestation Length?
- Parity (if you’ve had kids before GL: shorter)
- Age: older you are GL: shorter
- Genetics (maternal and paternal)
- Race/ethnicity
What myometrial changes occur in activation?
- Increase in CAPs - gap junctions - Prostaglandin receptors - Oxytocin receptors
What is the most common CAP in myometrial up-regulation?
Connexin 43
Actin/myosin cause ____ myometrial contractility and are antagonised with ____ channel blockers
Increased Calcium
Ca2+ voltage channels cause ____ myocyte excitability and are clinically blocked with _____
Increased B2 sympathomimetics
Gap junctions caused ____ intercellular connectivity and are antagonised with _____
Increased PG synthase inhibitors (COX1 and COX2)
Though serum progesterone levels do not change prior to labour, the ratio and activity of the progesterone _____ in the uterus change such that there is effectively a _____
Receptors Progesterone withdrawal
B-adrenergic agonists cause myometrial ____ by binding to adenyl cyclase linked receptors
Relaxation
What do Prostoglandins have to do with labour; and how do we stimulate labour with this knowledge
- Increase myometrial (muscle) contractility
- Lead to cervical changes
- associated with membrane rupture
So How do we induce labour from this?
So we can give PG as gel or tablet
Artifically rupture membranes → let the amniotic fluid run out
Put finger up to cervix, move finger around and take membranes off → PG release
What is Oxytocin?
Hormone nonapeptide from postpit. and genital tract
Syncinon is synthetic Oxytocin
Not essential for initiation of labour
Like PGs requires a gap junc. to be effective!
Used to induce and aument labour
Primary prevention of Post Partum Haemorrhage
Describe the model of cervical ripening
Can be due to preterm (eg infection) or fullterm (normal) and sets off a cascade of events that slowly leads to cervical change.
Starts with an inflammatory even that leads to the ECM of cervix being completel degraded, and cervix effectively “disappears” so baby can come out
Foetal membrane rupture occurs at the ______
Zone of altered morphology
What is happening at BIRTH
- We have Mature fetus and the timing is right
- Pelvic ligaments softened (extra +1cm on pelvic diameters)
- Uterus excitable and contractions coordinated
- cervix soft and easily dilateed
- Membranes may rupture; this gives more PGs and better mechanical benefits
What are the stages of labour?
Stages:
1st: until full dilatation (10cm) latent and active phase
2nd: full dilatation until birth of baby (1-2hours)
3rd: from birth of baby to delivery of the placenta
Not complete until placenta is out; otherwise mother will bleed out
The 1st stage of labour, what actually happens?
- CONTRACTIONS:
- last ~90 seconds, a pressure rise wave, with 45 seconds of pain in the middle past a specific high Pressure
- Cervical effacement and dilatation (to 10m)
- Descent of the presenting part into birth canal
- SRM- spontaneous rupture of membrane
- ROM- Rupture of membranes
- PROM- premature ROM
During the ___ component of a contraction there is no intervillous blood flow
Pain
During the ___ component of a contraction there is no intervillous blood flow
Pain
Where/ how does the baby “descend’ during the first stage
Into the pelvis (hopefully) curled up into a ball head first.
Partogram watches progress.
- Baby come into pelvic inlet transversely
- Does 90º turn in pelvic cavity
- Comes out
Importance of establishing continuous breathing at birth?
If a baby has a primary apnea; without intervention they will likely have another secondary apnea → Heart rate and blood pressure will drop.
90% transition easily
10% require some help to breathe
1% need major resuscitation
Involution of labour
Baby has come our and lactation has already commenced.
Involution is changes back to a non-pregnant state
Now we have:
- Placental seperation
- Cleavage through decidua basalis
- Contractions to prevent postpartum haemorrhage
- Increased uterine sensitivity to oxytocin
By 7 days postpartum, uterus had reduced 50% in weight
