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ESA 4 > Reproductive System Week 10 > Flashcards

Reproductive System Week 10 Flashcards

1
Q

Define parturition

A

The scientific term used to describe the transition from the pregnant state to the non-pregnant state at the end of gestation (birth) - includes all types of birth

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2
Q

Define labour

A

The non-scientific term used to describe parturition when both the cervix and the uterus have been remodelled (vaginal birth)
Does not include C section
Labour is a part of parturition
Lay people call parturition “labour”

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3
Q

From what point can the baby survive outside of the uterus, and therefore have legal rights?

A

24 weeks

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4
Q

If parturition occurs before 24 weeks what is this known as?

A

Spontaneous abortion (miscarriage)

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5
Q

What is meant by the term pre-term parturition?

A

Parturition before 36 weeks but after 24 weeks

The baby has potential to survive

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6
Q

What is meant by term parturition?

A

Parturition that occurs between 37-42 weeks of pregnancy

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7
Q

What is the term for parturition that occurs after 42 weeks of pregnancy?

A

Post-term parturition

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8
Q

What is the danger of preterm parturition?

A

Baby born too small, underdeveloped

Problems of viability and health - neuronal, gut, liver, lungs

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9
Q

What is the danger of post-term parturition?

A

Baby will become too large to deliver non-surgically
Baby may die in the uterus
Risk for mother and baby
Biggest cause of maternal mortality in the UK

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10
Q

What are some risks related to term parturition?

A

Infection
Size of the neonatal head v.s. The maternal pelvis
Blood loss

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11
Q

At what stage are mothers normally induced for labour?

A

41 weeks and 3 days

Drug or membrane rupture

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12
Q

What is the first stage of labour?

A

Regular painful contractions
Dilation, shortening and softening of the cervix
Ends when uterine cervix fully dilated
Latent phase - slow dilation of cervix to ~3cm
Active phase - dilation of cervix occurs more rapidly

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13
Q

What is the second stage of labour?

A

Begins at full dilation of the cervix and ends with complete delivery of the foetus
The pushing part

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14
Q

What is the third stage of labour?

A

Begins with completion of foetal expulsion
Ends with delivery of the placenta
Important
Effect of uterine contractions dramatically increases
Uterus contracts down hard
Shears off placenta and expels it
Normally occurs within ten minutes
Compresses blood vessels, reducing haemorrhage
Enhanced by giving oxytocic drug
Manual fundal massage

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15
Q

At what stage of pregnancy should the uterus be palpable above the pelvic symphysis?

A

12 weeks

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16
Q

At what stage of pregnancy should the uterus be palpable at the umbilicus?

A

20 weeks

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17
Q

At what stage should the uterus be palpable at the xiphisternum ?

A

36 weeks

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18
Q

What two foetal variables are the main influences of labour?

A

Foetal size
Foetal attitude - degree of flexion or extension of the head - optimal flexion 45 degrees - smallest possible diameter (9.5cm - suboccipitobregmatic diameter) presents at the pelvic inlet

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19
Q

Describe the different kinds of attitude that a foetus may have

A

Vertex, flexed (suboccipitobregmatic diameter) - head flexed to chest - 9.5cm
Sinciput, military (occipitofrontal diameter) - head straight - 11.5cm
Brow (occipitomental diameter) - head extended slightly - 13 cm
Face (submentobregmatic diameter) - head extended fully - 9.5cm

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20
Q

What is meant by the lie of the foetus?

A

The long axis of the foetus relative to the long axis of the uterus
Can be longitudinal, transverse or oblique

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21
Q

What is meant by the presentation of the foetus?

A

The orientation of the foetus - which pole of the foetus overlies the pelvic inlet
Can be cephalic or breech

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22
Q

Describe the types of breech presentation

A

Complete breech means the legs are bent - feet at the level of the baby’s bottom
Footling breech - One or both feet point down so that the legs would emerge first
Frank breech - Legs point up with feet by the baby’s head so the bottom emerges first

23
Q

What is meant by the position of the foetus?

A

The relationship of a nominated site on the presenting part of the foetus to a nominated location on the maternal pelvis - can be assessed most accurately on bimanual examination
Cephalic presentation the nominated site is the occiput
Breech presentation the nominated site is the sacrum

24
Q

What is meant by the term engagement?

A

The widest diameter has entered the pelvic inlet

25
Q

What is meant by the term station?

A

Refers to the leading bony edge of the presenting part relative to the maternal ischial spines as assessed on bimanual examination

26
Q

Describe the different types of female pelvis

A

Gynecoid (50% of women) - pelvic brim slightly ovoid or transversely rounded
Moderate depth
Sidewalls straight
Ischial spines blunt and somewhat separated
Sacrum deep, curved
Subpubic arch wide

Android (23% of women)
Heart-shaped, angular
Deep
Sidewalls convergent
Ischial spines prominent, narrow interspinous diameter
Sacrum slightly curved, terminal portion often beaked
Subpubic arch narrow

Anthropoid (24% of women)
Oval, wider AP than transverse
Deep
Sidewalls straight
Ischial spines prominent often with narrow interspinous diameter
Sacrum slightly curved
Subpubic arch narrow
Platypelloid (3% of women)
Flattened AP, wide transversely
Shallow
Straight sidewalls
Ischial spines blunted, widely separated
Slightly curved sacrum
Subpubic arch wide
27
Q

Which type of pelvis is the best for vaginal birth?

A

Gynecoid

28
Q

What is the typical diameter of the pelvic inlet?

A

11cm

Softening of ligaments may increase it

29
Q

Describe the first stage of labour

A

Myometrium tone changes to allow contractions of the body of the myometrium to increase intrauterine pressure
Large contractions of the uterine musculature (myometrium) occur
Regular, occur at shorter and shorter intervals and result in intrauterine pressures of 50-100 mmHg
Compared with about 10 mmHg between contractions
One of the functions of these contractions is to retract the lower uterine segment and cervix upwards to allow the vagina and uterus to become one continuous birth canal
Brachystasis - the property of myometrial cells whereby the shortening of each muscle cell during contraction is followed during relaxation by a failure to regain initial length - each subsequent contraction further shortens the cell - eventually each cell becomes much shorter and broader –> the fundal musculature becomes thicker and uterine volume decreases
The lower uterine segment does not take part in these contractions - passive during labour
Therefore the lower segment moves upwards and is retracted - can be palpated abdominally - junction between the uterine segments - retraction ring - contrast between thick and thin myometrium
The cervix becomes remodelled during pregnancy- becomes sufficiently compliant to allow expulsion of the neonate - cervix initially has high connective tissue content - rigid and resistant to stretch - collagen fibre bundles embedded in proteoglycan matrix - remodelling divided into softening, ripening, dilation and postpartum repaid
Cervix can no longer be pulled upwards because of its attachment to uterine and uterosacral ligaments and pubocervical fascia
Usually lasts between 7 (multiparous) and 13 (primiparous) hours

30
Q

What is brachystasis?

A

Brachystasis - the property of myometrial cells whereby the shortening of each muscle cell during contraction is followed during relaxation by a failure to regain initial length - each subsequent contraction further shortens the cell - eventually each cell becomes much shorter and broader –> the fundal musculature becomes thicker and uterine volume decreases

31
Q

Describe the second stage of labour

A

Fully dilated cervix is drawn up to just below the level of the pelvic inlet
Subsequent uterine contractions and the resultant decrease in uterine plume push the foetus through the pelvis
This process should last less than 1 hour

32
Q

Describe cervical remodelling

A

During pregnancy the cervix is of major importance in retaining the foetus in utero
High connective tissue content - collagen in proteoglycan matrix - rigid, resistant to stretch
Firmly closed cervical os
Divided into softening, ripening, dilation and postpartum repair

Softening - begins in first trimester of pregnancy and proceeds slowly thereafter - first measurable increase in tissue compliance but maintains cervical competence - gradual changes in intercellular matrix - structural changes to collagen bundling - glycosaminoglycan content increases as pregnancy progresses accompanied by a change in GAG composition
Ripening - occurs more rapidly in the weeks or days preceding birth - maximal increase in tissue compliance and decrease in integrity - features of a pro-inflammatory reaction - increased vascularisation, influx of monocytes and raised levels of Il 6 and 8 - hyaluronic acid (GAG) increases -

Dilation - during dilation hyaluronidase levels rise and break hyaluronic acid down into low molecular weight form –> contributes to increased viscoelasticity, tissue distensibility, hydration and disorganisation of collagen matrix - elevated activity of metalloproteinases also contributes to collagen breakdown –> softened consistency of cervix, shortened distance from foetal membranes to os (effacement) and greater pliability of the shortened cervical canal to distension, allowing the cervix to dilate sufficiently to allow passage of a term foetus

Postpartum repair - recovers tissue integrity and competency

33
Q

What regulates cervical remodelling?

A

Prostaglandins E2 and F2a have been shown to increase the compliance of the cervix, affect collagen bundle content and associations
PGE2 also induces leukocyte migration into the cervix by inducing release of IL8
Role for them in ripening at least but unsure about softening
Role for relaxin has been proposed - receptors detectable in cervical tissue
NO also a possible ripened - stimulates local release of PGs

34
Q

Describe the myometrium

A

Consists of bundles of non-striated muscle fibres intermixed with areolar tissue, nerves, blood and lymph vessels
Outer longitudinal layer less distinct and is organised as intertwined muscle bundles surrounding blood vessels - perhaps important for haemostasis following placental delivery
Inner subendometrial myometrium blends into the endometrial stroma and is composed of short muscle bundles arranged in a circular pattern
During pregnancy oestrogens stimulate an increase in myometrium bulk, initially by increasing numbers of myocytes, but primarily by increasing myocyte size from about 50 to 500 micrometres (hypertrophy) and glycogen deposition
Functionally behaves as a syncytium - coupled electrically via specialised gap junctions or nexuses - coordination of the spread of current and contraction through the myometrium

35
Q

Describe myometrium contractions during pregnancy

A

Occur throughout pregnancy
Frequency, amplitude, duration and direction of propagation are much reduced during most of pregnancy but then increasing towards term
During parturition these contractions must be strong but periodic, not continuous, in order to prevent pressure occlusion of the blood supply to the conceptus
Must be spatially organised so that the contractions in the lower uterus do not prevent entry into the birth canal
Contraction depends on rose in intracellular calcium concentration - liberation from intracellular stores and entry from extracellular fluid
Calcium binds regulatory sites on the contractile proteins, actin and myosin, to allow expression of ATPase activity and hence contraction
The release of calcium is stimulated by the presence of action potentials within the muscle cell
Spontaneous depolarising pacemaker potentials occur - if the magnitude of such potentials exceeds a critical threshold –> burst of action potentials i superimposed on the pacemaker - sharp increase in intracellular calcium occurs –> contraction
Calcium then pumped back into intracellular stores and out of the cell –> muscle relaxes
Contractility can be modulated by changing the pacemaker potentials or the relationship between these potentials and the threshold for spiking, the effect of spiking on calcium release –> contractility, interconnectivity of myocytes –> spread of contraction
All three contribute to the increased myometrial activity as parturition approaches
Due to the activity (direct or indirect) or PGs and oxytocin
PGF2a and oxytocin destabilise the membrane potential, reducing the threshold for spiking
PGE2 and PGF2a enhance calcium entry into the cells and Oxytocin acts mainly by enhancing the liberation of calcium from intracellular stores –> increased contractility
Oxytocin and PGF2a - increase connectivity among myocytes through increased connexin links –> facilitating spread of contractile waves
PGI2 - relaxes smooth muscle - potentially ensures periods of relaxation between contractility to maintain foetal blood supply - may also relax the lower uterus

36
Q

How thick is the myometrium during pregnancy?

A

2-3cm thick

37
Q

How do uterine contractions vary between early pregnancy and labour?

A

Early pregnancy - low amplitude, every 30 mins
Middle - less frequent than labour contractions - higher amplitude - Brixton hicks - brings the muscle fibres together to act as syncytium

Labour:
Early - variable, higher amplitude
Late - higher frequency and higher amplitude

38
Q

What is the clinical definition of labour?

A

Three contractions that last for 1 minute or more within 10 minutes

39
Q

What are prostaglandins?

A

Biologically active lipids
Synthesised in most body tissues
Local hormones acting at or near their site of synthesis
Inactivated in the lung during one circulation in the bloodstream

40
Q

What are the main prostaglandins produced by utero-placental tissues?

A

PGE2, PGF2a and PGI2

41
Q

What factors increase PG synthesis?

A

Alteration of the stability of membranes binding phospholipase A2 - liberating the active enzyme
Oestrogens activate phospholipase A2

42
Q

Which steroid hormone inhibits phospholipase A2, decreasing PGs?

A

Progesterone

43
Q

What is the effect of high progesterone and thus low PGs during pregnancy?

A

Quiescent uterine environment

44
Q

What is the effect of the increasing oestrogen:progesterone ratio around labour?

A

Increased production of arachidonic acid
Increased PG synthesis
Increased frequency and intensity of contractions

45
Q

What is the effect of the oestrogen:progesterone ratio on the sensitivity of the myometrium to oxytocin?

A

Oestrogen increases the number of oxytocin receptors, whereas progesterone decreases them
Oestrogen makes the tissue more sensitive to oxytocin
Oxytocin receptors, upon binding oxytocin, cause the release of endometrial PGs directly
Therefore the oestrogen:progesterone ratio can effect PG release independently of circulating oxytocin levels

46
Q

What is oxytocin?

A

Nonapeptide
Synthesised by magnocellular neurones in the supraoptic and paraventricular nuclei of the hypothalamus and transported axonally to the posterior pituitary gland for release into the blood
It is also synthesised in several other tissues, including the decidual tissue and to lesser extents in the amnion and chorion
Oestrogens are the main up-regulators of oxytocin synthesis by uteroplacental tissues as labour progresses

47
Q

How do oxytocin levels vary during pregnancy?

A

Blood levels in pregnant women are low until term approaches when plasma oxytocin levels vary diurnally - nocturnal peak corresponding to a peak of uterine spontaneous activity
Blood oestrogen levels are thought to correlate with this circadian uterine activity - suggesting uterine origin for the blood oxytocin
During labour, short duration blood-borne pulses of oxytocin of increasing frequency occur - peaking in stage 2 - seem to originate at least in part from posterior pituitary
Ferguson reflex - release of oxytocin from the posterior pituitary is stimulated by distension of the uterine cervix via a neuroendocrine reflex - sensory nerves from vagina and cervix linked to pituitary release of oxytocin - At the same time oxytocin receptors increase on the myometrium due to oestrogen:progesterone ratio increase –> positive feedback - in addition uterine stretching promotes the appearance of receptors for PG and oxytocin under low progesterone conditions - stretch induced response promotes transition to parturition

48
Q

How large is the cervix at full dilation?

A

10cm

49
Q

What triggers labour?

A

Debated
In sheep - rise in cortisol triggers high oestrogen:progesterone ratio - triggering the cascade of events
Plasma cortisol concentrations in the human foetus and in the amniotic fluid do rise during the last few weeks of human pregnancy
However foetal adrenal hypoplasia doesn’t necessarily lead to post maturity - parturition in normal range has been seen with congenital absence of adrenal glands
Also maternal infusions of ACTH or synthetic glucocorticoids do not apparently induce parturition in women
maternal and foetal blood levels of CRH do rise exponentially towards term but only in humans and great apes - most of this rise seems to originate from the placenta - rises exponentially in third trimester - peaking at delivery
Binding protein for CRH also decreases towards term, increasing the bioavailability of CRH
Pre and post maturity are associated with faster or slower rising levels of CRH respectively
CRH may then act within the foetoplacental unit to stimulate output of foetal pituitary aCTH and cortisol by direct action on foetal zone of the foetal adrenal
Cortisol then stimulates further placental CRH production - positive feedback
CRH also stimulates foetal adrenal output of DHEAS - substrate for progesterone and oestrogen
Maternal plasma progesterone concentrations do not generally fall at human parturition - and the oestrogen:progesterone ratio does not show a reliable increase
However antiprogestins initiate parturition in women
Possible that local rise in the ratio as opposed to circulating levels are more important
Changes in the local metabolic stability or interconversion of steroids have been proposed
The ratio of progesterone receptor B (Activating) to A and C (repressors) found to decline towards term
Also During labour steroid 5beta-reductase expression and activity fall - reduce levels of a potent relaxation inducing metabolite of progesterone - 5beta-dihydroprogesterone - coupled with change in receptors - blinds uterus to some actions of progesterone
One consequence of this is rise in uterine expression of oestrogen receptor as parturition approaches
Therefore uterus sees a shift of increasing oestrogen:progesterone
Stimulus for these changes is unclear

50
Q

How can labour be induced and when would you do this?

A

Once the cervix is sufficiently dilated (bishop score >6)
Prostaglandins infused via vagina
Oxytocin - often also given to women delivering naturally to ensure powerful myometrial contractions - reduce postpartum haemorrhage
Progesterone receptor antagonists can also be used
Amniotomy - artificial rupture of the membranes - may be sufficient on its own to induce labour - more effective if used with oxytocin - shortens the interval from induction to delivery by 1-3 hours but doesnt lower the rate of cesarean
Sweeping - digital separation of the foetal membranes from the lower uterine segment prior to labour at term - may accelerate the onset of labour by releasing endogenous prostaglandins - majority of studies show no significant increase in women going into labour within 7 days
Mechanical dilators - significantly shorten induction to delivery interval - as effective as PGE2 - hygroscopic dilators rely on absorption of water to swell and forcibly dilate cervix
Single technique rarely effective on its own - combination may be required

51
Q

How is the physiological state of the foetus monitored during labour?

A

Heart rate:
- Scalp electrode
- Doppler
Foetal scalp sampling

52
Q

Describe some operative vaginal delivery procedures

A

Forceps

Vacuum

53
Q

Is an episiotomy recommended by NICE?

A

No, heals better if tears along the weakest point

54
Q

What are the indications for a C section and what route is usually taken?

A 
Failed induction of labour
Failure to progress (dystocia) - most common
Cephalopelvic disproportion
Previous uterine surgery
Prior uterine rupture
Outlet obstruction
Placenta Praevia, placental abruption
Foetal distress
Cord prolapse
Foetal malpresentation (transverse lie)

Transverse hysterotomy is most common - lower blood loss, heals strongest

ESA 4 (28 decks)

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