Pregnancy Blood Work: What You Need to Know

Aug 18, 2021

Pregnancy Blood Work:
What You Need to Know

Pregnancy results in profound and amazing biochemical changes. The pregnant body physiologically adjusts to benefit both parent and baby. These changes are reflected in pregnancy blood work, and your awareness of these changes allows you to interpret markers more accurately and provide better support to your clients.

Pregnancy leads to decreases
in RBC, HGB, and HCT

If your pregnant client has lower than optimal red blood cells (RBC), hemoglobin (HGB), and hematocrit (HCT), it may not be anemia. Decreases in these markers are more than likely a reflection of exactly what should be happening with pregnancy blood work.

When a person becomes pregnant, they experience a completely normal increase in the plasma volume of their blood. Red blood cells also increase, but not in proportion to the increase in plasma volume. This is often termed “dilutional anemia” or “physiologic anemia of pregnancy.” Essentially, the red blood cells are diluted as a result of the increase in plasma volume, hence the decrease in RBC, HGB, and HCT on the blood work (1, 2).

Therefore, in order to accurately analyze blood work for your pregnant clients, the reference ranges for these markers should be adjusted downward to reflect these normal decreases during pregnancy.

Why does plasma volume increase during pregnancy?

Increases in plasma volume support fetal growth and development, while also decreasing the chance of hemorrhage during delivery (1). This phenomenon occurs due to sodium and water reabsorption by the kidneys, pregnancy-related increases in progesterone and aldosterone, and adaptations in the cardiovascular system. It’s reasonable to deduce that any abnormalities in these functions might influence blood volume increases and thus RBC, HGB, and HCT levels.

Obesity, preeclampsia, long-term hypertension, iron deficiency, idiopathic fetal growth restriction, caloric, and specifically protein restriction have all been shown to affect plasma volume expansion. Lupus nephritis and advanced diabetes may also be problematic.  An awareness of these issues, generally, and their effect on volume expansion, specifically, can help you support your clients to avoid negative obstetric outcomes.

Let’s look at how plasma volume, RBCs, and HCT change throughout pregnancy

Plasma volume begins to increase at about 6 weeks of gestation, peaks at around 32 weeks, and plateaus until delivery. Red blood cells (erythrocytes) gradually increase without a plateau until delivery.

The interplay of plasma volume and red blood cells is why hematocrit eventually begins to increase around 32 weeks in the chart below (1).

After delivery, plasma volume decreases as a result of diuresis and blood levels of RBCs and HCT return to pre-pregnancy levels. However, due to hormonal signaling, plasma volume increases again 2 to 5 days later and remains somewhat elevated for approximately 4 to 6 months.

pregnancy blood work

As a result of these typical changes, red blood cells, hemoglobin, and hematocrit ranges must be adjusted on pregnancy blood work (3).

LabSmarts appropriately and proportionately adjusts the reference ranges for RBC, HGB, and HCT downward to account for dilutional anemia of pregnancy while also accounting for trimester!

We are the only blood chemistry analysis software that accounts for these trimester-dependent changes.

pregnancy blood work

How do I know if it’s true anemia or physiological anemia on pregnancy blood work?

This is a complicated question, but LabSmarts can help. True anemia is more easily recognized due to LabSmarts’ strict pregnancy blood work analyses. But your clinical skills also play a role. If your client has a history of iron, vitamin C, or vitamin B12 anemia, if they are vegetarian, or if they have long-term digestive inflammation then it may be that they are experiencing true anemia. Remember, if they suffer from one of the issues that hinder plasma volume expansion—obesity, preeclampsia, long-term hypertension, idiopathic fetal growth restriction, caloric/protein restriction, lupus nephritis, and advanced diabetes—then true anemia may also be more apparent as physiological anemia isn’t as likely to occur.

If you’d like LabSmarts’ help in determining true versus physiological anemia in pregnancy blood work, click here to try the software and learn more!


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