A pregnant mother undergoes significant changes in
acid-base status as well as
sodium and
calcium metabolism to combat her physiological needs of pregnancy. Pregnant patients experience mild
respiratory alkalosis due to the stimulation of the respiratory center by
progesterone. This is associated with a corresponding increase in
bicarbonate excretion by kidneys; as a result, the pH remains slightly high (7.40-7.45) but within the normal range. Pregnant women are predisposed to
starvation ketosis as compared to nonpregnant states due to relative
insulin resistance and increased production of the counter-regulatory
hormone. Physiological mild
hyponatremia occurs during pregnancy due to increased AVP secretion caused by resetting of osmoreceptors in the hypothalamus at a lower osmolality, but values below 130 mEq/L require a diagnostic workup and intervention.
Gestational diabetes insipidus can occur due to increased production or decreased destruction of
enzyme vasopressinase. Secretion of
parathyroid hormone-related peptide by the placenta and breasts and two- to three-fold increased
calcium and
phosphate absorption in the maternal gut are the key changes in
calcium metabolism during pregnancy. Though rare, both hypo- and
hypercalcemia in pregnancy are associated with significant maternofetal morbidity and mortality.
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