Lecture 13: Parturition - Normal birth

Question 2

What are the three P’s of labour?

Answer 2

• Passage
• Power
• Passenger

Question 3

Challenges in Human Parturition?

Answer 3

• 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

Question 4

What is the principle hormone to maintain quiescence?

Answer 4

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

Question 6

What affects Gestation Length?

Answer 6

• Parity (if you’ve had kids before GL: shorter)
• Age: older you are GL: shorter
• Genetics (maternal and paternal)
• Race/ethnicity

Question 7

Challenges in Human Parturition?

Answer 7

• 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

Question 8

What is the principle hormone to maintain quiescence?

Answer 8

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

Question 10

What affects Gestation Length?

Answer 10

• Parity (if you’ve had kids before GL: shorter)
• Age: older you are GL: shorter
• Genetics (maternal and paternal)
• Race/ethnicity

Question 11

What myometrial changes occur in activation?

Answer 11

• Increase in CAPs - gap junctions - Prostaglandin receptors - Oxytocin receptors

Question 12

What is the most common CAP in myometrial up-regulation?

Answer 12

Connexin 43

Question 13

Actin/myosin cause ____ myometrial contractility and are antagonised with ____ channel blockers

Answer 13

Increased Calcium

Question 14

Ca2+ voltage channels cause ____ myocyte excitability and are clinically blocked with _____

Answer 14

Increased B2 sympathomimetics

Question 15

Gap junctions caused ____ intercellular connectivity and are antagonised with _____

Answer 15

Increased PG synthase inhibitors (COX1 and COX2)

Question 16

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 _____

Answer 16

Receptors Progesterone withdrawal

Question 17

B-adrenergic agonists cause myometrial ____ by binding to adenyl cyclase linked receptors

Answer 17

Relaxation

Question 18

What do Prostoglandins have to do with labour; and how do we stimulate labour with this knowledge

Answer 18

• 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

Question 19

What is Oxytocin?

Answer 19

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

Question 20

Describe the model of cervical ripening

Answer 20

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

Question 21

Foetal membrane rupture occurs at the ______

Answer 21

Zone of altered morphology

Question 22

What is happening at BIRTH

Answer 22

• 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

Question 23

What are the stages of labour?

Answer 23

Stages:

1^st: until full dilatation (10cm) latent and active phase
2^nd: full dilatation until birth of baby (1-2hours)
3^rd: from birth of baby to delivery of the placenta

Not complete until placenta is out; otherwise mother will bleed out

Question 24

The 1st stage of labour, what actually happens?

Answer 24

• 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

Question 25

During the ___ component of a contraction there is no intervillous blood flow

Answer 25

Pain

Question 26

During the ___ component of a contraction there is no intervillous blood flow

Answer 26

Pain

Question 27

Where/ how does the baby “descend’ during the first stage

Answer 27

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

Question 29

Importance of establishing continuous breathing at birth?

Answer 29

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

Question 30

Involution of labour

Answer 30

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