Hematocrit

The hematocrit is often used with the hemoglobin test to assess for anemia in pregnancy. But, what does it mean if hematocrit is high? Is a low hematocrit always iron deficiency? The hematocrit test is a tool to help assess for anemia in pregnancy, but may also give clues to overall maternal health. 

Hematocrit Testing

The Hematocrit (HCT) is a measure of the volume of packed red blood cells (RBCs) in the centrifuged sample.

Hematocrit = individual erythrocyte volumes X erythrocyte count/10

It is an essential component of a complete blood count (CBC), that is expressed as a percentage.

Hematocrit in Pregnancy

Hematocrit percentages decrease by approximately 2% in the first half of pregnancy due to increasing plasma to RBC ratios. This decrease can be greater in multifetal gestations. More important than the percentage number is the drop that should occur from the first trimester through second trimester with hemodilution.

Postpartum changes may depend on birth experience. There may be an initial drop due to blood loss during delivery, followed by a gradual return to pre-pregnancy levels. Generally, ranges recover and return to prepregnancy ranges by 6 weeks postpartum.

High Hematocrit in Pregnancy

Elevated hematocrit of >44% increases the risk of adverse pregnancy outcomes.

​Studies show that a hematocrit greater than 40% increases the risk of pregnancy complications and a hematocrit that doesn’t drop by approximately 2% from the first trimester to the late second trimester also increases the risk of pregnancy complications.

Causes of High Hematocrit in Pregnancy

• Dehydration
• Hypoxia
• Hypothyroidism
• Polycythemia Vera
• Iron Overload/Hemochromatosis 

Low Hematocrit in Pregnancy

Low hematocrit can indicate anemia and should be assessed further with other complete blood count indices.

In much of conventional obstetrical and midwifery care, the classic H&H (hemoglobin and hematocrit) is all that is run in assessing for prenatal anemia. This is tragic, as many cases of low hemoglobin and hematocrit are not associated with iron deficiency and primary treatment for low H&H is iron supplementation. ​

Causes of Low Hematocrit in Pregnancy

• Anything than can cause a decrease in the production of red blood cells can be a cause of lower hematocrit percentages. See Red Blood Cell Article. 
• Thiamine Deficiency
• Overhydration

Want to Know More...

Advanced Lab Analysis in Pregnancy

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The content in this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your medical condition. ​

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