Definition
Pregnancy is known to be a state of “physiologic anemia” due to the disproportionate increase in plasma volume relative to red blood cell volume. This increase in blood volume is necessary to supply the fetus and placenta and begins very early in pregnancy. The plasma volume is already increased by 10-15% at 6 weeks of gestation and increases to 30-50% greater than pre-pregnancy volume by term. The red cell volume, in contrast to this, is only increased by 20-30% at term. This increase is prompted by a higher level of erythropoietin. Thus, despite a higher red cell volume, the hematocrit will fall during pregnancy. The greatest time of disproportion between the plasma volume and red cell volume changes will be at 28-36 weeks. Anemia during pregnancy is defined differently than someone who is not pregnant. To be considered anemic during pregnancy the hemoglobin needs to be less than 11g/dL in the 1st or 3rd trimesters.
Other hematologic changes in pregnancy include an increase in white blood cells, particularly neutrophils, and a slight decrease in platelet count. The average white cell count during pregnancy is about 9-15k. It increases up to term, and can go as high as 25k during labor. Platelets, on the other hand, remain in the normal non-pregnant range but mean platelet counts may be slightly lower than in healthy non-pregnant women. The “low normal” range is considered to be about 106-120k.
There are also many changes in blood chemistries during pregnancy as well, mostly by the same dilutional mechanism as the hematocrit. Important among these are albumin, total protein and creatinine. Both albumin and total protein decrease by about 1g/dL by mid-pregnancy and creatinine decreases by about 0.3mg/dL. For other chemistry changes, see chart (below).
| Test | Nonpregnant Range | Pregnancy Effect | Gestational Timing |
|---|---|---|---|
| Blood Chemistry | |||
| Albumin | 3.5-4.8 g/dL | 1 g/dL decrease | By midpregnancy |
| Calcium | 9.0-10.3 mg/dL | 10% decrease | Falls gradually |
| Chloride | 95-105 mEq/L | No change | |
| Cholesterol | 200-240 mg/dL | 50% increase | Rises steadily |
| Creatinine | 0.6–1.1 mg/dL | 0.3 mg/dL increase | By midpregnancy |
| Fibrinogen | 200–400 mg/dL | 1.5-3x increase | By term |
| Glucose, fasting | 65–105 mg/dL | 10% decrease | Gradual fall |
| Potassium (plasma) | 3.5–4.5 mEq/L | 0.2–0.3 mEq/L decrease | By midpregnancy |
| Protein (total) | 6.5–8.5 g/dL | 1 g/dL decrease | By midpregnancy |
| Sodium | 135–145 mEq/L | 2–4 mEq/L decrease | By midpregnancy |
| Urea nitrogen | 12–30 mg/dL | 50% decrease | First trimester |
| Uric acid | 3.5–8 mg/dL | 33% decrease | First trimester |
| Urine Chemistry | |||
| Creatinine | 15–25 mg/kg/d | No change | |
| Protein | Up to 150 mg/d | Up to 250–300 mg/day | By midpregnancy |
| Creatinine clearance | 90–130 mL/min/1.73 m2 | 40–50% increase | By 16 weeks |
| Serum Enzymes | |||
| Alkaline phosphatase | 30–120 U/L | 2x to 4x increase | By 20 weeks |
| Amylase | 60–180 U/L | Controversial | |
| Creatinine phosphokinase | 26–140 U/L | 2- to 4-fold increase | After labor (MB bands as well) |
| Lipase | 10–140 U/L | No change | |
| Aspartate aminotransferase (AST) | 5–35 mU/mL | No change | |
| Alanine Aminotransferase (ALT) | 5–35 mU/mL | No change | |
| Formed Elements of Blood | |||
| Hematocrit | 36–46% | 4–7 point decrease | Nadir at 30–34 weeks |
| Hemoglobin | 12–16 g/dL | 1.4–2.0 g/dL decrease | Nadir at 30–34 weeks |
| Leukocyte count | 4.8–10.8 x 103/mm3 | 3.5 x 103/mm3 increase | Gradual increase to term, as high as 25 x 103/mm3 in labor |
| Platelets | 150–400 x 103/mm3 | Slight decrease | Gradual |
Subspecialty
Related Media
Keyword history
See Also:
Pregnancy: Heme and electrolyte changes
