Maternal physiology Flashcards
What is human chorionic gonadotrophin?
A glycoprotein with molecular weight of 39000
Which cells secrete hCG?
Trophoblast cells of the implanting conceptus
What are the functions of hCG?
Maintains the corpus luteum in the early weeks of pregnancy by facilitating the continued production of progesterone and oestrogen.
Promotes steroidogenesis and foetoplacental unit.
May have a role in stimulating testicular secretion of testosterone and gonadal differentiation.
What constitutes weight gain for the pregnant mother?
Foetus 3.5kg
Placenta 0.65kg
Amniotic fluid 1kg
Uterus 1kg
Breasts 0.5kg
Plasma and red cells and fluid retention 2kg
Maternal fat 4kg
By how much does total blood volume increase during pregnancy?
1.5L (30-40%) mostly by 34 weeks
What are some changes to blood volume and composition during pregnancy?
- Plasma increases
- Red cell mass increase
- Drop in haematocrit - the red cell mass increases but the plasma increases more, causing a drop in haematocrit
- More oxygen can be carried due to increased RBCs
- White cell count increases to fight infection
- Platelets increase
What are the consequences of decreased albumin concentration in pregnancy?
Colloid osmotic pressure falls –> glomerular filtration rate increases –> predisposes the woman to oedema due to reduced osmotic pressure as fluid is more likely to leave the vessels
Which globulins increase during pregnancy?
Thyroid binding globulin, corticosteroid binding globulin, angiotensinogen, transferrin
Which factors help blood coagulate more readily?
Increased fibrinogen
Clotting factors II, VII, VIII, IX, X increase
Platelet turnover increases
Antithrombin III falls (an inhibitor of clotting factors)
Fibrinolysis falls
What are advantages of blood coagulating more readily?
Less likely to haemorrhage post-delivery
Less likely to have a massive bleed if the placenta becomes detached
What are disadvantages of blood coagulating more readily?
More likely to get clots in the legs
Thrombotic embolism
What is noteworthy about CVS changes during pregnancy?
They are primary events not secondary to demand.
Why does blood pressure fall in mid pregnancy but rise to normal at term?
Because total peripheral resistance falls due to vasodilation mediated by oestrogen, progesterone and prostaglandins.
Why is blood pressure measured during antenatal visits?
Because if BP rises before it should it can indicate problems with the pregnancy such as hypertension or pre-eclampsia.
Why is venous pressure in the lower limbs increased?
1) Mechanical compression by the uterus
2) Haemodynamic effect due to increased uterine blood flow: more blood going to uterus –> joins onto the venous return to the heart –> becomes harder for the blood in the legs to get back to the heart because there is so much blood flowing through the veins
What is supine hypotension?
Low blood pressure when lying flat on the back
Why is lying flat on the back problematic?
Pregnant uterus falls down upon the inferior vena cava and obstructs flow, can cause fainting and discomfort.
Pregnant women should lie on side, not back. Should be left side (20% increase in CO), right side (10% increase in CO).
Which organs does blood flow increase to?
Breast, uterus (90% to placenta and 10% to uterine wall and vagina), skin (thermoregulation) and kidneys
By how much do renal blood flow and plasma flow rise?
30% and 45% respectively
Which hormone causes increase in renal function?
Relaxin
Why does GFR increase by 50%?
Due to increase RPF and fall in plasma colloid osmotic pressure
What happens to plasma creatinine and urea levels?
Decrease
What is glycosuria and when may it occur?
Glycosuria = glucose in the urine. May occur if the filtered glucose load exceeds re-absorptive capacity. Because the filtration rate is so high, you can filter out more glucose than can be reabsorbed.
Why may amino acid excretion increase?
Amino acids are usually filtered out in the glomerulus and completely reabsorbed. During pregnancy, filtering out increases so cannot be completely reabsorbed.
What is the ultimate result of these changes in renal function?
Net sodium retention
Which factors promote sodium retention?
1) Activation of the renin angiotensin system
2) Rise in aldosterone
3) Oestrogen
4) Cortisol
Which factors promote sodium loss?
1) Rise in GFR
2) Expanded plasma volume
3) Progesterone rise
4) Prostaglandin rise
Why is water retained?
Due to rise in plasma osmolarity, anti-diuretic hormone is released, helping you retain water and make the urine more concentrated. During pregnancy, the threshold osmolarity for the release of ADH becomes lower.
Why is there dilation of renal pelvis and ureters?
Due to extra fluid flowing through the kidneys and due to progesterone.
Why is there increased frequency of urination?
Due to increased GFR, bladder hyperaemia and irritation of the bladder by the enlarging uterus.
What is minute ventilation?
Tidal volume x respiratory rate
Increases up to 50% in pregnancy
What is PaCO2?
Partial pressure of arterial CO2 and falls to about 30mmHg at term.
Causes mild respiratory alkalosis as there is less CO2 in the blood.
Why does the thoracic cage expand?
Due to the softening of the thoracic ligaments. The costovertebral angle widens. This means that the lungs can expand more even though the diaphragm is elevated.
Why does the diaphragm elevate?
Relaxant effect of progesterone and increased abdominal contents.
What happens to residual volume?
Falls by 20%
What is the effect of reduced functional residual capacity?
Reduces the amount that tidal volume is diluted with each breath
What happens for FVC and peak expiratory flow?
Both increase
What happens to FEV1?
Unchanged
Why do pregnant women feel breathless?
This is dyspnoea of pregnancy and is thought to be a central effect of progesterone. They are not actually hypoxic.
Why is maternal appetite stimulated?
Central effect of progesterone as it is an orexigenic hormone (stimulates appetite). This is coupled with the fact that pregnant women become resistant to leptin, which is normally produced in fat cells and inhibits your appetite.
What is the effect of generalised decrease in gut motility?
Prolonged transit time of food and increased water absorption. Causes constipation thus why a high fibre diet is recommended.
What is the effect of reduced lower oesophageal tone?
Reflux and heart burn
What is the effect of impaired gallbladder contraction?
Increased stone formation
What are some other gastrointestinal changes?
Cravings
Morning sickness
Increased saliva secretion
Increased iron and calcium absorption
Position of small and large intestine is changed
What are some changes that occur to carbohydrate metabolism?
Insulin secretion increases
Blood glucose levels fall in 1st trimester
Insulin resistance develops in late pregnancy
What is the cause of such carbohydrate metabolism changes?
Due to human placental lactogen
* Reduces peripheral insulin sensitivity
* Mobilizes free fatty acids from fat stores
* Free fatty acids are converted to glucose which is transported to the foetus
What is the risk of these changes to carbohydrate metabolism?
May develop gestational diabetes
Outline changes to protein metabolism
About 500g is retained by full term
High protein diet necessary
Plasma amino acid levels fall
Outline changes to fat metabolism.
Fat is the main energy store
Plasma free fatty acids and cholesterol rise
Glycogen stores are low
Ketosis (an accelerated starvation response) may occur
