76 Maternal physiology changes so dramatically during pregnancy that reference intervals for biochemical tests in non-pregnant women are often not applicable. The main differences in commonly requested tests are shown in Table 76.1. These differences should not be misinterpreted as indicating that some pathology is present. Table 76.1 Reference intervals in the third trimester of pregnancy, and how they compare with non-pregnant controls
Pregnancy
Maternal physiology
Serum/blood measurement
Pregnant
Non-pregnant
Potassium (mmol/L)
3.2–4.6
3.5–5.3
Chloride (mmol/L)
97–107
95–108
Bicarbonate (mmol/L)
18–28
22–29
Urea (mmol/L)
1.0–3.8
2.5–7.8
Glucose (fasting) (mmol/L)
3.0–5.0
4.0–5.5
Adjusted Calcium (mmol/L)
2.2–2.8
2.2–2.6
Magnesium (mmol/L)
0.6–0.8
0.7–1.0
Albumin (g/L)
32–42
35–50
Bilirubin (µmol/L)
<15
<21
Alanine aminotransferase (U/L)
3–28
3–55
Aspartate aminotransferase (U/L)
3–31
12–48
Alkaline phosphatase (U/L)
174–400
30–130
Blood H+ (nmol/L)
34–50
35–45
Blood PCO2 (kPa)
3.0–5.0
4.4–5.6
Weight gain
Pregnancy
