Changes in Maternal Physiology During Pregnancy

There are a number of changes in maternal physiology during pregnancy that are summarised in this article.

## Contents

* 1 Weight Gain
* 2 Cardiovascular Changes
* 3 Renal Changes
* 4 Respiratory Changes
* 5 Gastrointestinal Changes
* 6 Metabolic Changes
* 7 See also

## Weight Gain[edit]

* 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[edit]

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[edit]

* 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[edit]

* 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[edit]

* 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[edit]

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)

## See also[edit]

* Common Maternal Complaints During Pregnancy