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6. OBSTETRICS > Anatomy, Physiology & Labour > Flashcards

Anatomy, Physiology & Labour Flashcards

1
Q

What is the pelvic inlet?

A

The upper border of pubic symphysis, iliopectinal line, ala of sacrum and the sacral promontory.

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2
Q

What is the mid pelvis?

A

Apex of pubic symphysis, ischial spines, sacrospinous ligament and tip of sacrum

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3
Q

What is the pelvic outlet?

A

Subpubic arch, ischial tuberosities, sacrotuberous ligament and coccyx

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4
Q

In which plane are the pelvic inlet and pelvic outlets the widest?

A

Inlet: widest in transverse plane
Outlet: widest in A-P plane

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5
Q

What are the 4 types of female pelvis?

A

Gynaecoid (50%)
Anthropoid (25%) - favours OP presentations
Android (20%) - prominent ischial spines, narrow subpubic arch, difficult to pass larger babies
Platypoid (3%)

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6
Q

How do you calculate EDD?

A

First day LMP + 9 months + 1 week

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7
Q

What are the gestational weeks of the 3 trimesters?

A

1st trimester = 1-12 weeks
2nd trimester = 13-28 weeks
3rd trimester = 29-40 weeks

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8
Q

How does weight gain differ in the 1st trimester compared to the 2nd and 3rd trimester?

A

1st trimester mostly placental weight gain (placenta requires ↑ oxygen, glucose & blood flow for growing fetus). Mother prepares for metabolic demands of later pregnancy (fat & protein deposition).

2nd and 3rd trimester mostly foetal weight gain - mother prepares for delivery & feeding.

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9
Q

When does fetal growth accelerate / peak?

A

Growth accelerates from ~12 weeks and reaches a maximum rate at ~30-36 weeks.

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10
Q

What endocrine changes occur in pregnancy?

A

Increased oestrogen + progesterone (largely mediated by placental hormone production)

Prolactin converts ductal cells to alveolar cells

Human placental lactogen (HPL) – fatty acid metabolism

Parathyroid hormone (PTH) – more calcium required due to kidney excretion

Cortisol changes

Aldosterone increases: upregulation of RAAS - increase in blood volume (salt + water retention)

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11
Q

What metabolic changes occur in pregnancy?

A
  • Increased protein metabolism & deposition (fetal, placental, maternal tissue)
  • Growth of breasts, uterus & musculature
  • Increased maternal fat reserves
  • Increased relative insulin resistance & increased carbohydrate metabolism ( ↑ circulating glucose in late pregnancy & glucose delivery). Placenta releases anti-insulin factors into maternal circulation: hPL/hCS, placental growth hormone, oestrogen & progesterone: risk of gestational diabetes & excessive fetal growth
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12
Q

What happens to BP during pregnancy? Why?

A

Falls from 1st - 2nd trimester, reaches minimum by 20 weeks then rises again to pre-pregnancy level in 3rd trimester (~36 weeks).

Oestrogen causes generalised vasodilation (increases local NO & prostacyclin) which REDUCES peripheral RESISTANCE. Also progesterone-mediated FALL in peripheral resistance.

  • Pathological blood pressure problems tend to be more evident in 3rd trimester as physiologically this is when BP increases.
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13
Q

What happens to cardiac output during pregnancy? Why?

A

Increases ~↑50% in first trimester

Due to increases in blood volume (40-50%), heart rate & stroke volume (due to increased preload)

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14
Q

What haematological changes occur in pregnancy?

A

Increased plasma volume (50%)
Increased red cell mass (20-30%)

Relative anaemia picture because red cell mass does not increases as much as plasma volume (haemodilution, decreased Hb conc. and risk of anaemia)

Increased coagulation factors (especially fibrinogen & VIII) & WHITE CELL COUNT (up to 20)

Pregnancy often described as ‘prothrombotic’ state: thrombotic risk is highest in post-partum period (much higher than risk of COCP

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15
Q

What renal changes occur during pregnancy?

A

Increased GFR (50%) - due to ↑CO, ↑ renal blood flow, ↑ increased urinary flow

Increased Na⁺ reabsorption: influenced by angiotensin II, aldosterone, oestrogen & arginine vasopressin

Reduced threshold of hypothalamic osmoreceptors: plasma osmolarity more dilute (~10mOsm/kg lower) -normally, this would decrease ADH secretion to allow more fluid loss, however, as osmoreceptors have reduced threshold, increases in osmolality result in increased thirst and increased ADH (more fluid retained)

Total body water increases (comprises largest part of maternal weight gain: ½ in plasma, ½ in interstitial fluid -risk of oedema).

Glycosuria (saturated reabsorption)

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16
Q

What respiratory changes occur during pregnancy?

A

Increased tidal volume (~40%) to meet increased oxygen consumption: deeper breathing, increased air flow for increased alveolar O₂ absorption

Leads to ↓ maternal CO₂ - mild respiratory alkalosis, assists diffusion of CO₂ from fetal blood to maternal blood (across placenta)

Early adaptation: progesterone & oestrogen act on medullary respiratory centres (note: respiratory rate, vital capacity and inspiratory reserve volume do not change)

Increased maternal pulmonary blood flow (~40%): due to increased CO, more blood to absorb O₂ from lungs

Increased O₂ carrying capacity of blood due to ↑ red cell mass & 2,3-DPG (an anion that displaces O2 from Hb and increases O2 to tissues)

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17
Q

What skin changes occur during pregnancy?

A
  1. 70% blood flow increase to skin = warmer/clammier. vascular changes = spider naevi, palmer erythema, variscosities.
  2. Increase in pigmentation (linear nigra, chloasma)
    3 Striations (striae gravidarum)
  3. Dermatoses (pruritis, eczema, PEP- polymorphic eruptions, pemphigoid).
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18
Q

What GI changes occur during pregnancy?

A
  1. Early pregnancy: nausea & vomiting (hCG mediated)
  2. Increased gastric emptying and reduced gastro-oesophageal sphincter tone (acid reflux)
  3. Decreased colonic motility (constipation).
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19
Q

What musculoskeletal changes occur during pregnancy?

A

Posture, balance & gait – prone to falls, injuries and musculoskeletal pain (e.g. pelvic girdle pain). Effects of hormones on joints, soft tissue remodelling.

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20
Q

Which hormones dominate in pregnancy?

Which hormones dominate in labour?

A

Relaxins in pregnancy: progesterone, relaxin and NO.

Progesterone is responsible for uterine quiescence, hyperpolarises myometrial cells and inhibits prostaglandin synthesis

Stimulants in labour: oestrogen, oxytocin, prostaglandins and placental corticotrophin-releasing hormone (CRH)

The oestrogen-primed uterus is sensitive to stimulants.

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21
Q

What is the role of prostglandins in labour?

A

Prostaglandins: PGF₂α and PGE₂
o Paracrine Action
o Production & receptors stimulated by oestrogen
o Potentiates contractions induced by oxytocin
o Produced by fetal membranes & maternal decidua

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22
Q

What is the role of oxytocin in labour?

A 
Oxytocin: 
o	Hormonal Action
o	Produced in maternal & fetal posterior pituitary
o	Receptors induced by oestrogen
o	Stimulates PGF₂α action
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23
Q

What is Ferguson’s reflex?

A

Neuroendocrine reflex

Upon application of pressure to the internal end of the cervix, oxytocin is released (therefore increase in contractile proteins), which stimulates uterine contractions, which in turn increases pressure on the cervix (thereby increasing oxytocin release, etc.), until the baby is delivered (stimulation of nerves on pelvic floor generates urge to push).

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24
Q

How are changes to the cervix brought about during labour?

A

Elastin > collagen. PGE2 degrades collagen fibres: more elasticity. Oestrogens stimulate proteolytic enzymes (break down collagen fibres & change shape of cervix)

Relaxin: widens cervix, part of dilation process

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25
Q

What is Bishop’s score (i.e. how is it calculated)

A

Measures: position (2), consistency (2), effacement / length(3), dilation (3) and station (3)

+1 for each previous vaginal birth, -1 for first time birth

26
Q

What do different Bishop’s score indicate?

A

Score >8 indicates cervix is ripe and high chance of spontaneous labour or response to induction

<5 indicates labour will not begin without induction
<3 indicates labour will not respond to induction

27
Q

How does a membrane sweep work? When is it offered?

A

By detaching the chorionic membrane from the decidua: release of local prostaglandins. Introduce fingers into os and pass circumferentially around the cervix (if won’t admit finger, massaging around cervix in vaginal fornices may achieve similar effect).

Must be offered prior to formal induction, and offered at 40 & 41 (nulliparous) and 41 (parous) week antenatal visits. Additional membrane sweeping may be offered if labour does not start spontaneously. Can be performed by midwives, repeated ~36 hours.

28
Q

What are the indications for induction of labour?

A

If pregnancy outcome (mother, baby or both) will be improved if it is artificially interrupted rather than allowed to follow its natural course

Most common indications:

  1. Post-term (macrosomia: may offer from 41, don’t want to exceed 42)
  2. Pre-labour ruptured membranes
  3. Maternal diabetes: usually induced around due date (39) but if gestational diabetes let them go beyond)

Other indications: PET, IUGR

29
Q

Before commencing induction of labour, what needs to be done?

A

Record Bishop score & confirm normal FH rate pattern. Inform that likely more painful than spontaneous labour, discuss analgesia.

30
Q

What are different methods of inducing labour?

A

May be used in combination:

  • Artificial rupture of membranes (ARM).
  • PgE2 tablet / gel / controlled-release pessary,
  • Syntocinon
    (Misoprostol or mifepristone should only be offered to women who have intrauterine fetal death).

Mechanical methods: balloon catheters, laminaria tents – not for routine use.

31
Q

What is the preferred method for induction of labour?

A

Vaginal PGE2 is preferred unless specific reasons (e.g. risk of hyperstimulation). One cycle vaginal tablets or gel = one dose followed by 2nd dose after 6 hours if labour not established (maximum of 2 doses). One cycle of controlled-release pessary = 1 dose over 24 hours.

Surgical methods (ARM) = amniotomy +/- oxytocin (syntocinon injection) - only used if specific clinical reasons for not using vaginal PGE₂

32
Q

How should a woman be monitored after vaginal PGE2?

A

When contractions begin: assess with continuous electronic fetal monitoring (once CTG confirmed normal, use intermittent auscultation unless clear indications for continuous monitoring, and if fetal HR abnormal after PGE2, follow guidelines for fetal compromise)

Bishop score should be reassessed 6 hours after vaginal PGE₂ tablet or gel insertion, or 24 hours after controlled-release pessary insertion

If woman returns home after vaginal PGE₂, should contact obstetrician/midwife when contractions begin, or if no contractions after 6 hours.

33
Q

What is failed induction of labour?

A

Labour not starting after one cycle of treatment. Subsequent management options include a further attempt to induce labour and a caesarean section.

34
Q

What are complications of IoL?

A
  • Uterine hyperstimulation (consider giving tocolysis)
  • Cord prolapse during amniotomy (palpate for umbilical cord presentation during vaginal examination & avoid dislodging baby’s head, avoid procedure if head is high)
  • Check no signs of low-lying placental site before membrane sweeping & before induction of labour
  • Uterine rupture: requires emergency caesarean section

Note: induction associated with longer labours, higher rates of epidurals and higher operative delivery rates. When performed in women with previous CS it is associated with higher rates of uterine scar dehiscence.

35
Q

What is the first stage of labour?

A

Onset of regular uterine contractions (in association with progressive cervical change) up to full dilation.

Latent phase: until fully effaced and 4cm dilated
Active phase: regular contractions and dilation from 4cm

(note - multigravida may not be fully effaced but active phase is defined as 4cm dilation).

36
Q

How would you expect the first stage of labour to progress?

A

In active phase, delay in progress if:

Nulliparous: <2cm dilation every 4 hours (0.5cm/hour).

Multiparous: <2cm dilation every 4 hours (0.5cm/hour) OR slowing of progress

Note: not just dilation - also descent and rotation of head, changes to contraction (e.g. minimal change in cervix but previous OP at -2 now OA and at level of spines - not considered delayed).

37
Q

What is a partogram?

A

Documentation of maternal observations, FH, uterine activity, liquor, descent (station: relationship to imaginary line drawn at ischial spines) & cervical dilation.

Alert lines monitor dilation progress, if plot crosses an action line attempts should be made to improve progress.

38
Q

How is the first stage of labour managed?

A

Management of the latent phase: reassure, adequate hydration, nutrition, mobilisation & bladder care. Support of a birth partner has been shown to improve outcomes.
If low risk, semisolid food may be allowed (clear fluids preferred) - not allowed if any potential risks identified.

Management of active labour: VE every 4 hours (document on partogram).

39
Q

How is delay in the first stage of labour managed?

A

Transfer to obstetric-led care and ensure adequate hydration, bladder care, nutrition, analgesia.

Amniotomy if membranes intact, reassess after 2 hours, (if in community: may do ARM and reassess after 2 hours before transferring), consider oxytocin infusion.

NICE: oxytocin increases contraction frequency and strength, expedites time of delivery but won’t alter mode of delivery – continuous CTG due hyperstimulation risk: aim for 4 contractions / 10 mins, reassess after 4 hours.

40
Q

What is secondary arrest? What is obstructed labour?

A

Secondary arrest = no change in cervical dilatation after 2 hours following a period of normal active phase dilation

Signs of obstructed labour: delay in progress, excess moulding & haematuria

41
Q

When might a CS be indicated in the first stage of labour?

A

If there is still no change following syntocinon infusion or if there are signs of obstruction

42
Q

What are the first 5 key stages of labour (in terms of fetal positioning)?

A
  1. Descent (towards pelvic brim in either LOT or ROT position, ~38 weeks but may not occur until labour established in multigravidous)
  2. Engagement (when widest part of head deep in pelvis - <3/5ths palpable)
  3. Neck flexion (pressure down fetal spine, occiput contacts with pelvic floor, causes fetal neck flexion)
  4. Internal rotation (pelvic floor has forward and downward slope / V shape, each contraction creates rebound effect supporting small degree of rotation until 90 degree turn to OA position completed - commonly completed by start of 2nd stage)
  5. Crowning (after widest diameter passes through narrowest point of pelvis - head no longer retreats between contractions).
43
Q

What is the diameter of the presenting part of the fetus dependent on?

A

Fetal size

Presentation: part of fetus lying at pelvic brim. Affected by attitude: position of baby’s body (fully flexed, deflexed, extended)

Position: relationship of the denominator (occiput, mentum or sacrum) to the maternal pelvis.

Malformations: (hydrocephalus, large SOL e.g. teratoma, neck tumours preventing flexion)

44
Q

What are the different types of fetal presentation?

A

Vertex (flexed): Suboccipital bregmatic (SOB: 9.5cm) or Suboccipital frontal (SOF: 10cm) - “normal”

Vertex (neutral flexion): Occipitofrontal (OF: 11.5cm)

Brow: mentovertical (MV 13.5cm) - not deliverable

Face: submentovertical (SMV 11.5cm) or submentobregmatic (SMB)- mentoanterior will deliver but not mentoposterior

Breech: sacrum - deliverable but potential difficulties

Shoulder: not deliverable vaginally

45
Q

How does flexion affect the presenting part?

A 
SOB / SOF - baby completely flexed
OF - fails to flex
MV - if further extension
SMV - if further extension
SMB - if even further extension
46
Q

How is fetal attitude assessed when the head presents?

A

Check for posterior fontanelle (can see triangle). If can feel both fontanelle, head is DEFLEXED (neutral). If completely flexed can only see one fontanelle (posterior most common)

47
Q

What are the different fetal positions (in vertex presentation)?

A

LOA / ROA = left/right occipitoanterior
LOP / ROP = left/right occipitoposterior
LOT / ROT = left/right occipitotransverse

Most common = LOA

48
Q

During labour, what is the ideal power (uterine contractions)?

A

3-4 regular contractions every 10 mins (optimises power)

<2 every 10 mins = inadequate (too irregular/incoordinate to facilitate progress)

> 5 every 10 mins = hyperstimulation
lasting >2mins = tetanic contraction

Hyperstimulation and tetanic contractions both associated with tachysystole (fetus gains O2 during diastole, not enough time in diastole to receive sufficient O2 - hypoxia risk) and are ineffective (muscle fibres can’t work effectively).

49
Q

What is moulding in labour and why is it important?

A

Fit of foetal head through pelvis

No moulding: sutures a little apart
1+ sutures together but no gap
2+ sutures overlap but reduce with gentle pressure
3+ sutures overlap and do not reduce with gentle pressure

Excess moulding = sign of obstructed labour. Diameter compressed is diminished and the perpendicular diameter is elongated.

50
Q

What is the 2nd stage of labour?

A

From full dilation to delivery of baby

Passive 2nd stage: full cervical dilation before or without involuntary expulsive contractions

Active 2nd stage: baby visible, expulsive contractions with full dilation, or active maternal effort following confirmed full cervical dilatation in absence of expulsive contractions

51
Q

How long is the 2nd stage of labour expected to last?

A

Passive stage: if epidural in situ then 1 hour given to allow descent & optimise opportunity of spontaneous vaginal delivery. If no regional anaesthesia & no urge to push (despite confirmed full dilatation) then allow 1 hour and reassess.

Active stage: delay if >2 hours nulliparous and >1 hour multiparous

(expect most nulliparous to deliver within 3 hours of starting active 2nd stage, and most multiparous women to deliver within 2 hours)

52
Q

How is delay in the 2nd stage of labour managed?

A

Remember: adequate analgesia and assessment of fetal well-being throughout 2nd stage

Amniotomy if membranes intact

? adequate contractions if nulliparous - syntocinon if inadequate

Obstetric review: instrumental delivery, caesarean section

53
Q

What are the last 4 key stages of labour (in terms of fetal positioning?)

A
  1. Extension of the presenting part (occiput slips beneath subpubic arch, allowing head to extend until jaw delivered- head now born facing maternal back)
  2. Restitution (where head may externally rotate to face maternal thigh - occurs if fetus aligning head with shoulders while shoulders still negotiating pelvic outlet)
  3. Internal rotation (shoulders rotate from transverse to AP position)
  4. Lateral flexion (downward traction assists delivery of anterior shoulder below subpubic arch, upward traction assists deliver of posterior shoulder, then trunk born by lateral flexion).
54
Q

What are the degrees of perineal tear?

A

1st degree: perineal skin only

2nd degree: perineum involving perineal muscles but not the anal sphincter

3rd degree:

  • 3a <50% external anal sphincter (EAS) torn
  • 3b >50% EAS torn
  • 3c both EAS and IAS torn

4th degree: injury to perineum involving anal sphincter complex and anal epithelium

55
Q

What is an episiotomy and when is it used?

A

Right medio-lateral (or sometimes median) perineal incision involving perineal muscles. LA around vagina before incision (or top up epidural if already given). Pressure applied to stop bleeding & stitches given – should heal < 1 month.

Not routine: approximately 1 in 7 vaginal deliveries. May prevent a severe tear or assist delivery (allows baby to pass through). NICE recommends consideration of episiotomy if: baby is in distress and needs to be born quickly or delivery requiring forceps or ventouse, risk of severe tear to anus.

56
Q

What is the 3rd stage of labour?

A

From birth of baby to delivery of placenta + membranes

Placental separation: retraction causes oblique fibres to shorten causing clamping of blood vessels. The septa tears and veins in the spongy layer of the decidua become tense and burst. Villi collapse as blood is release (small gush of vaginal blood signifies placental separation). The ‘living ligatures’ retract to seal off blood vessels, blood vessels collapse and blood tracks between the placenta and decidua to complete separation.

57
Q

When and how is the third stage of labour managed physiologically?

A

Only recommended for low risk deliveries

No uterotonics, once cord stops pulsating, clamp cord and ask woman to push (delivery by maternal effort)

58
Q

When and how is the third stage of labour managed actively?

A

Recommended for high risk labours particularly if risk of PPH

Uterotonics: syntocinon or syntometrine IM (if normal BP)

Clamp cord early, controlled cord traction with guarding of the uterus.

  • Deferred cord clamping recommended for up to 5mins in active 3rd stage to enable extra blood volume to the baby improving iron stores. However, associated with higher risk of neonatal jaundice so not recommended if baby already at additional risk (e.g. maternal diabetes).
    (note: adverse events of controlled cord traction include cord rupture and uterine inversion with resultant massive postpartum haemorrhage)
59
Q

What are complications of the 3rd stage of labour?

A

PPH: >500mls from genital tract within 24 hours of delivery
o minor 500-1000mls
o major >1000mls (can now be split into 1000-2000 and >2000mls).

Retained placenta: >30 mins if active management, >60 mins if physiological
- Manual removal of the placenta (MROP): under anaesthesia in theatre - epidural, spinal or GA (GA preferred if heavy bleeding)

60
Q

Fetal monitoring

A

add some stuff

61
Q

Pain relief

A

add some stuff

62
Q

Assisted delivery

maybe C section?

A

add some stuff

6. OBSTETRICS (7 decks)

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