Pregnancy

3.2.3. Physiology

3.2.3.1.4.10. Pregnancy

Thus,

Chronic respiratory alkalosis which is compensated by renal excretion of bicarbonate

Typical blood gases results in the third trimester are:

Reduction in bicarbonate
--> Slightly reduced ability to buffer a metabolic acid load

Lower pCO2 would shift the oxygen dissociation curve to the left

But minimal change in pH

Increased 2,3 DPG levels during pregnancy

Overall,

Nausea and vomiting occur commonly in the first trimester
May be severe (hyperemesis gravidarum) and intractable vomiting
--> Fluid loss and electrolyte disturbances

Typically causing metabolic alkalosis

NB:

The actual acid-base effect of vomiting depends on the actual mix of acidic gastric fluid and alkaline intestinal secretions in the vomitus.
Alkalosis does not always occur with prolonged vomiting.

The pregnant woman is prone to develop elevated ketone levels because:

Fasting during pregnancy more rapidly results in hypoglycaemia and low insulin levels
Insulin resistance develops as pregnancy progresses (probably due to placental hormones)
Fasting ketosis develops in less than 16 hours in late pregnancy
* Compared to usually > 24 hours in the non-pregnant female

Ketones can cross the placenta and the foetus can adapt to use them as an energy source
Ketones may be important in myelination in the developing central nervous system
This mild ketosis that occurs with fasting does not seem to have any adverse effect on the mother
Effect of ketosis on foetus is uncertain

However,

Ketoacidosis due to maternal DM is more serious and has very serious adverse effect on the foetus

Diuretic use may cause a metabolic alkalosis
--> a mixed alkalosis because the hyperventilation has already reduced the pCO2