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Changes in Maternal Physiology (Gastrointestinal Changes (Maternal…
Changes in Maternal Physiology
Cardiovascular Changes
Cardiac Output
(↑) (stroke volume (↑) X heart rate (↑) ) -
1.5 L / min
.
Blood Pressure (in mid pregnancy)
↓
(total peripheral resistance ↓ x cardiac output ↑).
Total peripheral resistance
falls due to vasodilation by estrogen, progesterone and prostaglandins.
Venous Pressure in lower limbs ↑
Due to mechanical compression by uterus; haemodynamic effect due to uterus blood flow; veins more distensible because of progesterone.
Supine Hypotension
: low BP when lying on back.
Due to pregnant uterus falling down on vena cava.
Increase
of Blood Flow to:
Breast
Uterus - 90% to placenta, 10% to rest
Skin - thermoregulation
Kidneys ~ 30 %
No
blood flow change to brain,skeleton or gut.
Renal Changes
Renal
Blood
Flow ↑ 30%
Renal
Plasma
Flow ↑ 45%
(caused by relaxin)
Glomerular filtration rate ↑
50%
(Due to ↑ renal plasma flow and ↓ plasma colloid osmotic pressure)
Plasma Creatine
and
Urea Levels
↓
Glycosuria
(glucose in the urine) may occur.
Can be normal in pregnant women.
(because filtration by glomerulus exceeds reabsorption)
Amino Acid Excretion
↑
(because filtration by glomerulus exceeds reabsorption)
Overall changes:
Net Sodium Retention
Retained by:
Activation of the renin angiotensin system
Rise in aldosterone
Oestrogen
Cortisol
Lost by:
Rise in glomerular filtration rate
Expanded plasma volume
Progesterone rise
Prostaglandin rise
Water Retention:
When plasma osmolarity rises, ADH (anti-diuretic hormone) is released to help you retain water.
Urine becomes more concentrated.
Threshold osmolarity for release of ADH lowers during pregnancy.
Diuresis (increase of urination) occurs after delivery.
Dilation of renal pelvis and ureters
due to extra fluid flowing through kidneys + progesterone.
↑ Frequency of Urination
(first 6 weeks then subsides then recurs late in pregnancy due to compression of bladder by uterus)
Due to ↑ glomerular filtration rate, bladder hyperaemia, irritation of bladder by enlarging uterus.
Respiratory Changes
Minute Ventilation
(tidal volume x respiratory rate) ↑ - up to 50%
Tidal volume ↑ but respiratory rate is unaltered.
PaCO2
(partial pressure of arterial CO2) ↓
to about 30 mmHg at term.
Partly a central effect progesterone.
Causes mild respiratory alkalosis bc ↓ CO2 in blood.
Expansion of the Thoracic Cage
Due to the softening thoracic ligaments; widening of the costovertebral angle.
Allows lungs to expand more even w/ elevated diaphragm.
Elevated Diaphragm
~ 4 cm
Due to relaxant effect of progesterone and ↑ abdominal contents.
Residual Volume ↓
by 20%
Functional Residual Capacity
↓
Reduces the amount that tidal volume is diluted with each breath.
Forced Vital Capacity
(amount you breathe out in a single breath)
+ FVC%
and
peak expiratory flow
↑
FEV1
(volume that had been exhaled at the end of the first second of forced expiration) is unchanged.
Dyspnoea
(breathlessness)
Thought to be caused by progesterone.
Gastrointestinal Changes
Maternal Appetite Stimulated
progesterone is orexigenic (stimulates appetite)
pregnant women resistant to leptin
Cravings
Morning Sickness
(commonly in start of pregnancy)
Generalised decrease in Gut Motility
Reduced Lower Oesophageal Tone
Can cause reflux and heart burn
Impaired Gallbladder Contraction, ↑ Volume
Can cause increased stone formation.
↑ Saliva Secretion
↑ Iron and Calcium Absorption
Liver Size Unaltered
Alkaline phosphatase is elevated because of placenta and not liver.
Position of Small and Large Intestine Changed
Metabolic Changes
Carbohydrate Metabolism
Insulin secretion ↑
Blood glucose levels ↓ in 1st Trimester
Insulin Resistance Develops in Late Pregnancy
Changes mainly due to human placental lactogen
May develop gestational diabetes
↑ in Metabolic Rate
Protein Metabolism
~ 500 g retained by full term
High protein diet necessary
Plasma amino acid levels ↓
Fat Metabolism
Fat = main maternal energy store
Plasma free fatty acids and cholesterol ↑
Glycogen stores are low
Ketosis (accelerated starvation response) may occur
Weight Gain
Total
: 12.5 kg
Maternal Fat
~ 4 kg
Foetus
: 3 kg
Plasma, red cells and fluid retention
: 2 kg
Uterus
: 1kg
Amniotic Fluid
: 1 kg
Placenta
: 0.65 kg
Breasts
: 0.5 kg
Blood Volume and Composition
Total blood volume
increases by
1.5 litres (30-40%)
by 34 weeks.
Plasma
Increase ↑
1250 ml (45%)
(can be detected 6-4 weeks into pregnancy)
↓ in
haematocrit
(red cell mass increase < plasma increase) causing
dilational anaemia
. Helps pump blood more easily.
O2
carrying potential greater than consumption due to ↑ RBCs. Creates a reserve of O2
White cell count
increases (7000-10,000/11,000 /µl)
Platelet turnover
seemingly increases (reports vary)
Total plasma protein concentration
falls (7 to 5.5-6 g/100ml)
Albumin concentration
also falls resulting in colloid osmotic pressure ↓, glomerular filtration rate ↑, predisposition to odema
Globulins Increase
: Thyroid binding globulin, corticosteroid binding globulin, angiotensinogen, transferrin.
Blood coagulates more easily
:
Fibrinogen ↑
Clotting factors II,VII, VIII, IX, X ↑
Platelet turnover ↑
Antithrombin III falls (inhibitor of clotting factors)
Fibrinolysis falls
Cause of coagulation: estrogen's action on the liver
Adv:
less likely to have haemorrhage post-delivery
less likely to have a massive bleed if placenta becomes detached
Disadv:
More likely to get clots in the legs
Thrombotic embolism
Human Chorionic Gonadotropin
Structure
Glycoprotein with molecular weight - 39000
Secreted by trophoblast cells of the implanting conceptus.
α chain - had 92 amino acids, similar to α chain of LH, FSH and TSH.
β chain - has 145 amino acids. 97/145 are identical to β chain of LH.
∴ hCG has function similar to LH
Functions
Maintains corpus luteum in early weeks of pregnancy - allows continued production of oestrogen and progesterone.
Promotes steroidogenesis in foetoplacental unit.
May have role in stimulating testicular secretion of testosterone and gonadal differentiation.
Pregnancy Tests:
Pregnancy tests detect hCG in the urine.
Must have control line to determine whether the test is functioning.
Hormonal Overview
Estrogens
,
Progesterones
,
Human Chorionic Gondotrophin
(hCG)
, and
Human Placental Lactogen (hPL)
cause physiological changes in the mother which benefit the fetus.
hCG
- peaks
early
pregnancy
hPL and prolactin (PRL)
increase with
gestational age
