84 Effect of pregnancy on maternal physiology Flashcards
Uterus grows to occupy most of the pelvis by __ weeks, palpable abdominally from __ weeks
Uterus grows to occupy most of the pelvis by 16 weeks, palpable abdominally from 13 weeks
At term the uterus reaches what level?
Level of the xiphoid process (thorax widens as the ribs flare to accommodate organs)
What happens to structures on posterior abdominal wall during pregnancy?
Compressed when lying down
Changes to centre of gravity resulting in what during pregnancy?
Development an accentuated lumbar lordosis
=> Backache
Result of relaxin release during pregnancy?
Causes softening of ligaments
=> Sacroiliac and pubic symphysis pain
Anatomical changes to mother during pregnancy?
- Fist sized organ grows to occupy most of the pelvis by 16 weeks, palpable abdominally from 13 weeks
- At term uterus reaches the level of the xyphoid process (thorax widens as the ribs flare to accommodate organs)
- Compression of structures on the posterior abdominal wall especially when lying down
- Changes centre of gravity develop an accentuated lumbar lordosis. Leads to –> Backache
- Relaxin causes softening of ligaments. Leads to–> Sacroiliac and symphysis pubis pain
- Weight gain averages 12.5kg
Cause for 12.5kg weight gain in pregnancy?
- 6kg uterus, foetus and breast
- 3kg fat reserves for lactation
- Remainder is fluid
Result for pressure on IVC from foetus?
• Impedes venous return from LLs
• Impairs function of valves
=> Varicose veins
Cause for physiological anaemia in pregnancy?
Haematopoiesis is increased up to 30%
BUT
Increase in plasma volume (up to 50%) means that RBC count, haematocrit and haemoglobin conc are all reduced
Changes to WBC, platelets count and clotting factors during pregnancy?
- Small increase in WBC
- Unchanged platelet count, but more reactive
- Increase in clotting factors with thromboembolism risk
Circulatory adaptations to TPR during pregnancy?
• Uteroplacental circulation is characterised by high volume, low resistance flow
- Due to uterine spiral arteries and arterioles inability to vasoconstrict
• Pregnancy hormones = Reduce sensitivity to pressor agents (e.g. angiotensin) to vasoconstrict. => peripheral vasodilation occurs and TPR reduces
Result of peripheral vasodilation in pregnancy women?
Heat intolerance
Reduced TPR triggers what?
Triggers the renin-angiotensin-aldosterone system increasing blood volume
Effect of oestrogen in maintaining normal (low) blood pressure in foetus?
Vasodilation:
Oestrogen increases vascular endothelial growth factor (VEGF) and NO production in endothelial cells
What does VEGF mean?
Vascular endothelial growth factor
What do endothelial cell release in order to help maintain the low BP in the foetus?
Prostacyclin (prostaglandin I2 or PGI2)
- vasodilator
Changes to CO during weeks 6 -28 of pregnancy?
(CO = HR x SV)
Increases by 30-50%
- Increase in HR to 80-90/min
- Increase SV by ~ 10%
Which organs receive increased blood flow during pregnancy?
Uterus, breast and skin
Why is CO sensitive to posture during late pregnancy?
- Can fall because of IVC obstruction by uterus
* Resulting in hypotension/fainting when lying flat
At which point does the CO return to pre-pregnancy condition postpartum?
By 6 weeks
How is BP measured in pregnant women?
Measured semi-recumbent using Korotkoff phase 5 for diastolic
Related to changes in circulating plasma volume and peripheral resistance
Changes toBP in second trimester?
BP normally falls in second trimester
- Systolic falls ~5-10mmHg
- Diastolic falls ~10-15mmHg
What is pre-eclampsia?
Placental problem involving an increase in BP,
proteinuria and oedema
Potential cause for pre-eclampsia?
May involve failure of the 2nd wave of trophoblast invasion that normally impairs the capacity of maternal spiral arterioles to constrict (12-16 weeks)
Consequences of pre-eclapsia?
• Poor placental perfusion can cause foetal growth
restriction
• Increased vascular resistance in placenta causes:
– Decreased blood to placenta
– Hypertension in mother
– Renal arteriolar endothelial damage causes oedema, glomerular damage and proteinuria (‘acute atherosis’)
What is eclampsia?
Extreme hypertension (e.g. 180/120) • Increased intracranial pressure, seizures, coma • Significant risk of cerebral haemorrhage
Maternal mortality of eclampsia?
~ 8-36%
Interventions to treat eclampsia?
- Magnesium sulphate
- Antihypertensives
- Rapid delivery
- Careful fluid balance
Changes to respiratory system in mother during pregnancy?
• Progesterone increases sensitivity of central CO2 receptors • More ventilation • Increase in tidal volume by ~ 40% • Ventilation rate unchanged
Changes to renal system during pregnancy?
- Kidneys deal with foetal urea => increased renal function
- Increased glomerular filtration rate (GFR), as a result of increased CO, by ~30-50%
- Decreased plasma urea, creatinine and uric acid
- Bladder is compressed leading to frequent and urgent urination
- Ureters are dilated that can predispose to infection
Why is uric acid the most useful renal marker in pregnancy?
It rises before creatinine in response to renal impairment (e.g. pre-eclampsia)
Changes to total body water (TBW) during pregnancy?
TBW increases by ~6-8L
• Extracellular fluid (ECF) increases by ~3L, split between
plasma and interstitial fluid (ISF)
Changes to osmolality during pregnancy? Why?
Osmolality falls by ~10 mOsm/kg
• Decreased urea and creatinine
3 main changes to GI system in pregnant women?
- Morning sickness, nausea/ vomiting - esp. first 12-14 wks
- Constipation
- Gastric acid reflux, heartburn
Cause for morning sickness?
- Parallels HCG levels
* Worse in multiple pregnancy & hydatidiform mole
Cause of constipation in pregnant women?
- Pressure of uterus on rectum and lower colon
* Decreased motility, progestogenic effect on smooth muscle
Cause for gastric acid reflux in pregnant women?
- Relaxation of lower oesophageal sphincter
- Relaxation of GI smooth muscle (progestogenic effect)
- Pressure of uterus
- Worse lying down
- Aspiration risk during endotracheal intubation
What are the nutritional requirements of a pregnant women?
• Weight gain at term is ~7-14kg – Foetus 3.5kg – Placenta and amniotic fluid 1.5kg – Increased breast tissue 0.5-1kg – The rest is fat and extracellular fluid (ECF)
- Daily calorific requirement increases by ~15%
- 200-300 kcal/day
What happens in early pregnancy?
- Rate of growth of foetus relatively slow to 20 weeks
- ~3kg fat laid down to provide energy source for final trimester when growth is very rapid
- Maternal tissues more sensitive to insulin in early stages of pregnancy
- Increased protein synthesis
When does growth of foetus peak?
Between 30-36 weeks
What happens in later pregnancy?
- Relative insulin resistance, predisposing to ‘high-normal’ glucose levels
- Increased lipolysis supplying mother with source of energy
- Increase in circulating triglycerides stored in mammary tissue
- Increased requirement for protein
Gestational diabetes: • Spectrum? • Risk factors? • Predictor for? • Associations?
• Spectrum from normal to ‘impaired glucose tolerance’ to actual diabetes
• Risk factors:
– Race
– Obesity
– Family history
• Can be a predictor of future type 2 diabetes
• Associated with foetal macrosomia (increased insulin resistance; high glucose) and complications
Vitamin requirements of pregnant women?
- Folic acid needed for neural tube fusion (pre-conception)
- Vegetarians may need to increase B12 intake
- High levels of vit A may lead to foetal abnormalities
- Vit D supplementation is recommended
Mineral requirements of pregnant women?
Calcium;
• Maternal gut absorption increases
• Active transport across the placenta
• Increase in release from maternal bone
Role of zinc in pregnancy?
- Important role in many metabolic processes
- Protein synthesis
- Nucleic acid synthesis
- Synthesis/activity of insulin
- Increased dietary need, especially in vegans
Role of iron in pregnancy?
- Globally, high incidence of maternal iron deficiency
- If dietary iron low, may need supplements
- Supplementation with normal iron stores is undesirable, may increase oxidative stress
Placenta secretions?
- hCG has key role in maintaining pregnancy
* Other placental proteins and steroids
Endocrine secretions from the mother?
- Increased growth hormone release
- Decreased FSH and LH
- Increased prolactin
- Increased parathyroid hormone
- Pituitary increases in size (production of prolactin and ACTH and oxytocin)
- Thyroid increases in size due to hCG (similar in structure to TSH)
Postnatal changes to mother?
• Uterine involution complete by 6 weeks
• Amenorrhoea if breast feeding
– Duration related to frequency and duration of suckling
– May be associated with hot flushes and vaginal dryness
• Systemic changes largely reversed by 6 weeks
– Coagulation system changes may take longer
– Glucose tolerance normalises very rapidly
