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Flashcards in Labour Deck (60):
1

Parturition

Process of labour
begins much prior to actual onset of regular uterine contractions
uterus comproised predominantly of smooth muscle fibers

2

Phase 0 of labour

uterine quiescence
contractile tranquility

3

Phase I of labour

uterine preparedness
functional changes in myometrium + cervix

4

Phase II of labour

active labour
progressive cervical dilation and fetal delivery

5

Phase III of labour

uterine involution
fertility restored

6

Elements of Parturition

requires agents that stimulate onset of uterine regular contractions along with cervical effacement + dilatation

7

Uterotropins

agents that set the stage for regular uterine contractions and cervical change
estrogen
relaxin
Ca-dependent phospholipases
arachidonic acid (prostaglandin)

Progesterone counteracts actions of these uterotropins: maintains uterine quiescence

8

Uterotonins

agents directly involved in causing myometrial smooth muscle cells to contract
increased intracellular calcium in myometrium

oxytocin
prostaglandins (specifically PGF2alpha)
endothelin-1

9

Sheep model of labour

1) increased ACTH from fetal pituitary
2) increased cortisol from fetal adrenals
3) increased androgens from placenta (estrogen precursors)
4) increased estradiol in mother
5) decreased progesterone in mother

10

Parturition initiation in humans

however in humans, prior to onset of active labour (as opposed to sheep):
- serum progesterone levels do NOT fail
- serum estradiol levels do NOT rise
- administration of progesterone does NOT reliably prevent preterm labour
- administration of estrogen does NOT induce labour
- prostaglandins, arachidonic acid, relaxin, phospholipases, cortisol, oxytocin do NOT rise until active labour

11

Phase II of labour - prostaglandins

synthesized at/near site of action (interface of amnion/chorion and myometrium)

12

PGE2 i nlabour

cervical effacement
highest levels in amniotic fluid just below presenting part "forewaters"
breakdown of rigid structure of collagen fibers
unwinds collagen fibers
softens extracellular matrix
increased hyaluronic acid
decreased glycosaminoglycans

13

PGF2alpha in labour

Thinning of lower uterine segment during active labour --> inflammatory response in decidua --> arachidonic acid released
Process also stimulated by oxytocin

Leads to increase in intracellular calcium

14

Relaxin

peptide hormone originating from ovary
also involved in cervical ripening
unknown how it interacts with PGE2

15

Oxytocin

precursor produced in hypothalamus
secreted from post. pit in active labour
increase intracellular Ca (via activation of phospholipase C)
Oxytocin receptors present on myometrium:
- increase near term
- increased by estradiol: estrogen involved in labour induction
- down-regulated by progesterone through rest of pregnancy

Oxytocin used in late pregnancy (IV) for inducing labour
- not effective earlier on because fewer receptors

16

Myometrial contractions

muscle filaments: thick/thin filaments arranged in long random bundles to allow muscle shortening in any direction and maximize shortening

Gap junctions:
- transcellular membrane channels
- allow ion exchange between cells
- propagate electrical signal
- increase muscle shortening
- increase in number close to parturition
- increased by estradiol
- decreased by progesterone

17

Myometrial relaxation

decreased intracellular Ca
sequestration of Ca into SR
Dephosphorylation of myosin light chain
inactivation of myosin light chain kinase (by cAMP-dependent phosphorylation)
labour continuous process of alternating contractions/relaxations

18

Phase II clinical features

Lower uterine segment (passive segment + cervix) thinning and dilating
upper uterus (active segment) thickens with continuing uterine contractions

19

Summary of labour physiology

1) Cervical ripening
- stimulated by estradiol, arachidonic acid, PGE2
- inhibited by progesterone
2) contractions
- increased intracellular Ca due to PGF2alpha, oxytocin/oxytocin receptors
- increased # of gap junctions due to estradiol, inhibited by progesterone

20

Induction of labour

amniotomy
membrane sweeping (inflammatory action)
Foley catheter in cervix (increase mechanical pressure for prostaglandins)
oxytocin

21

Preventing preterm labour

NSAIDs
progesterone
Ca channel blockers

22

Evaluation of labour

Hx
Physical: vital signs
general exam
fetal heart rate
abdominal exam
SFH
Leopold maneuvers

23

Leopold maneuvers

1) palpate uterine fundus for contents
2) palpate fetal back on one side and limbs on other
3) palpate fetal presenting part just above symphysis
4) facing patients feet, determine fetal position (also confirmed on internal exam with a dilated cervix)

24

Occiput:

head flexed lowest part

anterior - facing maternal symphysis
45 degrees to symphysis on maternal left side - left occiput anterior
maternal sacrum - occiput posterior/OP

25

Lie of fetus

description of long axis of fetus relative to long axis of mother
longitudinal, oblique or transverse

26

Presentation of fetus

cephalic, breech or shoulder

27

Presenting part of fetus

part closest to cervix
occiput
face
brow
sacrum
lower limbs

28

Position of fetus

Orientation to maternal pelvis
e.g. left occipus anterior

29

Station of fetus

measure of degree of descent of presenting part (relation to maternal ischial spines)

30

Definition of labour

progressive cervical dilation, effacement, or both, resulting from regular uterine contractions every 5 minutes lasting 30-60 sec

31

1st stage of labour

onset of involuntary painful regular contractions to full dilation (10 cm)
latent/active phases

32

Latent phase - labour

onset of regular painful contractions q5 min lasting 30-60 sec
cervix

33

Active phase - labour

regular painful contractions q2-3 min lasting 45- 60 sec
cervix 3-4 cm to fully dilated (10 cm)
nulliparas: 1cm /hr
multiparas: 1.2 cm/hr

34

Second stage of labour

full dilation to delivery of fetus
maternal pushing increases forces directing fetus downwards and outwards
- push against a closed glottis
- increase intra-abdominal pressure
- descent of fetus into pelvis

Majority of pushing effort actually from uterine contractions, assisted by maternal pushing efforts

Nulliparas: 50 min - 3 h
multiparas: 20 min

35

Cardinal movements of delivery

minimize fetal diameter as they pass through narrowest diameters of pelvis
1) Engagement
2) Descent
3) Flexion
4) internal rotation
5) extension
6) external rotation/restitution
7) expulsion

36

third stage of labour

delivery of fetus to delivery of placenta
0-30 min (>90% deliver by 15 minutes)
blood clot forms at plane of cleavage
placenta slides into lower uterine segment
delivery occurs by maternal pushing and gentle traction on cord
management

37

Classic signs of placental separation

Gush of blood
lengthening of cord
fundus rises up
uterus becomes firm and globular

38

Active management of 3rd stage of labour

proven to reduce incidence of postpartum hemorrhage
uterotonics with delivery (oxytocin, misoprostol)
gentle, controlled cord traction
controversion - early cord clamping?

39

Pain in labour - early

Sensory impulses from lower uterine segment/cervix travel via visceral afferent nerve fibers to spinal cord, entering at T10-L1 nerve roots
- major pain pathway of first stage

40

Pain in labour - later first stage/2nd stage

once fetal presenting part has reached pelvic floor and during second stage, pain from pelvic structures and vagina travel via somatic afferent nerve pathways to L1-S4

Pain from perineum conducted through pain fibers of pudendal nerve - S2-S4
Pain relief in labour is affected by selective anesthesia of nerves involved

41

4th stage of labour

delivery of placenta to stabilization of maternal condition
1-1.5 h after delivery of placenta
bleeding slows
uterus remains contracted
maternal stabilization/bonding
first attempt at breastfeeding

42

Phase III of pregnancy

6 weeks following delivery
Most physiological changes return to non-pregnant state
uterine bleeding stops by contraction of muscle around vessels and thrombus formation
- decidua basalis remains with myometrium and becomes regenerated endometrial lining - no scar forms
superficial layer gets sloughed as lochia rubra, lochia serosa, lochia alba

43

Involution of uterus

gradual decrease in size of body of uterus (decrease in myometrial cell size, not #)
IMmediately after delivery of placenta, fundus palpable just below umbilicus: ~1 kg
Intermittent oxytocin release --> continues contractions (afterpains) - in response, uterus gradually decreases in size
3 weeks after delivery: uterus no longer palpable above symphysis; weighs ~300 g
4 weeks after delivery: returned to nonpregnant size, sloughed after 3 weeks
As endometrium regenerates, vascular bed covered over --> no scarring

44

Cervix post-delivery

cervix lengthens - external os remains funneled (multiparous os)

45

Lochia

normal vaginal discharge postpartum

46

Lochia rubra

originally red due to RBCs
4 days

47

Lochia serosa

after 4 days increasing leukocytes - pale

48

Lochia alba

after 10 days - normally yellow/white

49

Ejection of milk

suckling stimulates oxytocin
myoepithelial cells around alveoli in breast glands contract
milk ejected

50

Lactation

delivery of placenta
--> decreased estrogen/progesterone
--> increased PRL
--> milk production

51

Other physiological changes with peurperium

muscles of abdominal walls remain lax
- rectus muscles can separate: diastasis
- striae
Diuresis of increased circulatory volume
- eliminate increased blood volume in 1st week
- associated with increase in CO in first 48 hours
Reduction in size of pelvic blood vessels
reduction in coagulation factors: gradually fall over 6 weeks
Menses resume/fertility restored

52

Weight loss post-partum

Weight loss of ~15 kg;
- 7kg for baby, placenta, blood loss (immediate)
- 3kg for diuresis (over 2-5 days)
- 5kg for involution of uterus and decreased blood volume (over 5 weeks)

53

Resumption of menses

Absence of breastfeeding --> reduction in PRL level --> serum estrogen restored, ovulation resumes
may occur in 6-8 weeks postpartum
Phase III complete with resumption of menses

54

Postpartum hemorrhage definition

excessive bleeding in first 24 hours after delivery
vaginal delivery: >500 ml of estimated blood loss
C-section: >1000 ml
clinical definition = blood loss that can produce hemodynamic instability

55

Causes of postpartum hemorrhage

Tone
Tissue
Trauma
Thrombin

56

Tone in postpartum hemorrhage

atony --> most common cause of PPH (80%)

57

Risk factors of atony in PPH

failure to actively manage 3rd stage
uterine distention (due to polyhydramnios, twins, macrosomia)
uterine exhaustion --> precipitous labour, prolonged labour, high parity
infection --> prolonged rupture of membranes
function/anatomical distortion of uterus --> fibroid, previa prior to PPH
Bladder distention preventing uterine contraction

58

Tissue risk factors in PPH

Retained placenta
Succenturiate lobe
clots
abnormal placentation

leading to retained placenta, membranes, clot

59

Trauma risk factors in PPH

precipitous/operative vaginal delivery leading to vaginal, cervical or uterine injury

60

Thrombin risk factors for PPH

pre-existing/acquired risk factors (history of easy bruising, prior PPH, massive blood loss --> DIC)