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Flashcards in Anatomy, Physiology & Labour Deck (62)
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What is the pelvic inlet?

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


What is the mid pelvis?

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


What is the pelvic outlet?

Subpubic arch, ischial tuberosities, sacrotuberous ligament and coccyx


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

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


What are the 4 types of female pelvis?

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


How do you calculate EDD?

First day LMP + 9 months + 1 week


What are the gestational weeks of the 3 trimesters?

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


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

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.


When does fetal growth accelerate / peak?

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


What endocrine changes occur in pregnancy?

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)


What metabolic changes occur in pregnancy?

- 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


What happens to BP during pregnancy? Why?

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.


What happens to cardiac output during pregnancy? Why?

Increases ~↑50% in first trimester

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


What haematological changes occur in pregnancy?

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


What renal changes occur during pregnancy?

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)


What respiratory changes occur during pregnancy?

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)


What skin changes occur during pregnancy?

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)
4. Dermatoses (pruritis, eczema, PEP- polymorphic eruptions, pemphigoid).


What GI changes occur during pregnancy?

1. Early pregnancy: nausea & vomiting (hCG mediated)

2. Increased gastric emptying and reduced gastro-oesophageal sphincter tone (acid reflux)

3. Decreased colonic motility (constipation).


What musculoskeletal changes occur during pregnancy?

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


Which hormones dominate in pregnancy?

Which hormones dominate in labour?

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.


What is the role of prostglandins in labour?

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


What is the role of oxytocin in labour?

o Hormonal Action
o Produced in maternal & fetal posterior pituitary
o Receptors induced by oestrogen
o Stimulates PGF₂α action


What is Ferguson's reflex?

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).


How are changes to the cervix brought about during labour?

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


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

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

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


What do different Bishop's score indicate?

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


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

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.


What are the indications for induction of labour?

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


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

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


What are different methods of inducing labour?

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.