Reference intervals for anion gap and strong ion difference in pregnancy: a pilot study.
OBJECTIVE
Acid-base status and electrolyte levels change in normal pregnancy. We hypothesized that these physiological changes affect both anion gap and strong ion difference (SID).


METHODS
A cross-sectional study of normal pregnant women (6 in the first trimester, 47 in the second trimester, 59 in the third trimester, and 13 postpartum).


RESULTS
The anion gap in pregnancy (8.5 +/- 2.9 mEq/L) was less, compared to postpartum values (10.7 +/- 2.5 mEq/L), (p < 0.005). The SID, too, was lower (pregnancy, 38.3 +/- 2.9 mEq/L, postpartum 43.5 +/- 2.3 mEq/L, p < 0.001), reflecting the combined influence of changes in albumin, SID, and PCO(2).


CONCLUSIONS
Anion gap and SID both decrease in pregnancy, events which must be taken into account when managing acid-base disorders in gestation.
Akbari
Ayub
A
Department of Medicine, University of Ottawa, Ottawa, Ontario, Canada. aakbari@ottawahospital.on.ca
Wilkes
Peter
P
Lindheimer
Marshall
M
Lepage
Nathalie
N
Filler
Guido
G
D000136:Acid-Base Equilibrium / Q000502:physiology*; D005260:Female; D006801:Humans; D010865:Pilot Projects; D049590:Postpartum Period / Q000502:physiology; D011247:Pregnancy; D012016:Reference Values