Changes in Maternal Physiology During Pregnancy
From Conservapedia
There are a number of changes in maternal physiology during pregnancy that are summarised in this article.
Contents
Weight Gain
- Overall gain = ~12.5 kg
- Foetus = 3.5 kg
- Placenta = 0.65 kg
- Uterus = 1 kg
- Breasts = 0.5 kg
- Blood and fluid retention = 2 kg
- Maternal fat = 4 kg
Cardiovascular Changes
Blood volume
- Total blood volume increases by 1.5L (40%)
- Total plasma volume increases by 1.25L (45%)
- Total red blood cell mass increases by between 240ml (18% - without iron supplements) and 400ml (30% - with iron supplements)
- Haemocrit falls (40% to 31%)
- Haemoglobulin concentration falls from 13.5% to 11-12%
- Results in dilutional anaemia of physiological anaemia of pregnancy
- White blood cell concentration increases from 7000/ul to 10-11,000/ul
- Platelet turnover increases
- Total plasma proteins increase, but concentration decreases
- Globulin increases, albunin:globulin ratio falls
Cardiac Output
- Cardiac output increases by approximately 1.5L/min
- Stoke volume increases from 64ml to 71ml
- Heart rate increases from 70bpm to 85bpm
- Total peripheral resistance falls
- Blood pressure falls during first trimester, but returns to normal by term
Cardiac distribution
Increased flow to:
- uterus (from 50ml/min to 700ml/min, 90% to placenta)
- breasts
- kidneys (30%)
- skin
Venous pressure in lower body increased due to:
- mechanical pressure of uterus
- haemodynamic effect of increased flow to uterus
- veins more distensible (valves weakened) due to progesterone
Renal Changes
- Increased blood flow (40%)
- Increased plasma flow (45%)
- Increased glomerular filtration rate (50% - due to increased plasma flow and reduction in colloid osmotic pressure)
- Reduced levels of creatine and urea in plasma
- Failure to reabsorb all filtered glucose - glycosuria
- Amino acid excretion increased
- Increased sodium retention (largely due to activation of renal angiotensin system)
- Increased water retention
- In bladder frequency (both day and night)
- Due to increased GFR, compression by uterus and hyperaemia
- severe by week 6 then subsides until late pregnancy
Respiratory Changes
- Minute ventilation increases
- Respiratory rate constant
- Tidal volume increases - promoted by softening of thoracic ligaments and rising of diaphragm by 4 cm
- Functional residual volume decreases (reduces dilution of breath)
Gastrointestinal Changes
- Progesterone induces cravings
- Increased absorption of calcium and iron
- lower and upper intestines raised
- decreased motility of GIT (increased absorption, but leads to constipation)
- reduced tone of lower oesophageal sphincter (due to progesterone, leads to heartburn)
- increased volume and contraction of gull bladder (leads to kidney stones)
Metabolic Changes
Metabolism increases in general. Changes in:
- Carbohydrates (decrease in glucose levels in first trimester, increase in insulin resistance in third trimester due to human placental lactogen - induces metabolism of fat into glycogen which is diffused over placenta, but increases peripheral insulin sensitivity)
- Proteins (amino acid concentration falls due to active transport over placenta, require high fibre diet to compensate)
- Fat (fatty acids become main energy source and stores increase by 4 kg)
