5. Effect of Pregnancy on Maternal Physiology Flashcards
Increase in metabolic demands on the mother are met by….
hormone driven physiological adaptation
At term the uterus reaches?
The level of the xyphoid process
What happens to structures on post abdominal wall during pregnancy?
Compressed when lying down
Change to centre of gravity result in what during pregnancy?
Development of accentuated lumbar lordosis
==> Backache
Result of relaxin release during pregnancy?
Softening of ligaments.
–> Sacroiliac and symphysis pubis 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?
6kg uterus, foetus and breast
3kg fat reserve for lactation
Remainder is fluid
Result for pressure on IVC from foetus?
Impedes venous return from LL
Impairs function of valves results in varicose veins
Cause for physiological anaemia is 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. Hence peripheral vasodilation occurs and TPR reduces.
Result of peripheral vasodilation in pregnancy women?
Heat intolerance
Consequence of reduced TPR is pregnant women on RAAS?
Triggers RAAS and low blood pressure in vessels is detected.
This leads to increased blood volume.
Effect of oestrogen in maintaining normal blood pressure in foetus?
Oestrogen increases vascular endothelial growth factor 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)
Summary of changes to mother?
Anatomical changes
Circulatory adaptations: Blood volume, blood composition, TPR reduces, CO, bp, pre-eclampsia, eclampsia
Respiratory changes
Renal changes
Changes to CO during weeks 8-28 of pregnancy?
Increases by 30-50%
By..
-Increase in HR to 80-90/min
-Increase SV by about 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 normally post-partum?
after 6 weeks.
How is bp measured in pregnant women?
Semi-recumbent, using Korotokoff phase 5 for diastolic
Changes to bp in second trimester?
Systolic falls by 5-10mmHg
Diastolic falls by 10-15mmHg
What is pre-eclampsia?
Placental problem involving an increase in BP, proteinuria and oedema
Can begin around week 20
Potential cause for pre-eclampsia?
Failure of the second wave of trophoblast invasion. This normally impairs the capacity of maternal spiral arterioles to constrict. During 12-16 weeks.
Consequence to foetus of pre-eclapsia?
Poor placental perfusion can cause foetal growth restriction.
This increase vascular resistance in placenta causes….
1. Decrease blood to placenta
2. Hypertension in the mother
3. Renal arteriolar endothelial damage causes oedema glomerular damage and proteinuria (“acute atherosis”)
What is eclampsia?
Extreme hypertension (e.g. 180/120)
Leading to…
1. Increased intracranial pressure, seizures,coma
2. Significant risk of cerebral haemorrhage
Risk of eclampsia to mother?
Maternal mortality 8-36% (mainly in low resource countries as preventable by antenatal care)
Interventions to treat eclampsia?
Magnesium sulphate
Antihypertensives
Rapid delivery
Careful fluid balance
Changes to resp system in mother during pregnancy?
Progesterone increases sensitivity of central CO2 receptors
More ventilation
Increase in tidal volume by 40%
However, ventilation rate unchanged
Changes to renal system during pregnancy?
Kidneys deal with foetal urea and hence there is increased renal function
Increased GFR, due to increase CO
Decreased plasma urea, creatinine and uric acid
Bladder compression leads to frequent and urgent urination.
Dilated ureters can predispose to infection
Why is uric acid a good 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.
-ECF increase by about 3L, split between plasma and interstitial fluid
Osmolarity falls by about 10mOsm/Kg
-Decreased urea and creatinine
3 main changes to GI system in pregnant women?
Morning sickness, nausea/vomiting esp first 12-14 weeks
Constipation
Gastric acid reflux, heartburn
Cause for morning sickness?
Parallel hCG levels
Worse in multiple pregnancy
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
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
- Rest is fat and ECF
Daily calorie intake increase by 15% so 200-300kcal/day extra
- early pregnancy
• Rate of growth of foetus relatively ____ to 20 weeks.
• ~3kg fat laid down to provide energy source for final trimester when ____ is very rapid.
• Maternal tissues more sensitive to ____ in early stages of pregnancy.
• Increased protein _____. - later pregnancy
- Relative insulin resistance, predisposing to ‘high-normal’ _____ levels.
- Increased lipolysis supplying mother with source of _____.
- Increase in circulating triglycerides stored in ______ tissue.
- ______ requirement for protein.
- 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. - 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 weight gain findings?
Variance is much within, rather than between, populations
Emphasises the wide range of gestational weight gain associated with normal outcome.
Gestational diabetes:
- Spectrum?
- Risk factors?
- Predictor for?
- Associations?
Spectrum: Normal –> impaired glucose tolerance –> actual diabetes
Risk factors: Race, obesity, family history
Predictor: For future type 2 diabetes
Associated with foetal macrosomia (increased insulin resistance, high glucose) and complications
Vitamin requirements of pregnant women?
Vitamins:
- Folic acid needed for neural tube fusion
- 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 (calcification of skeleton).
– Maternal gut absorption increases (vit D3).
– Urinary loss decreases (parathyroid hormone).
– Increase in release of calcium from bone.
– Active transport across the placenta.
Role of zinc in pregnancy?
Protein synthesis Nucleic synthesis Nucleic acid synthesis Synthesis/activity of insulin Increased dietary need, especially in vegans
Role of iron in pregnancy?
High incidence of maternal iron deficiency, need for supplements
Supplementation with normal iron stores is undesirable. Leads to oxidative stress.
Placenta secretions?
hCG maintains pregnancy
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.
