Anemia in pregnancy: Clinical sciences

Anemia in pregnancy is characterized by a decrease in the hemoglobin in a pregnant patient. Now, a normal physiologic anemia of pregnancy occurs when both the red blood cell mass and plasma volume expand throughout gestation. However, the increase of red blood cells is disproportionately less than the increase in plasma volume, resulting in a dilutional anemia, or physiologic anemia of pregnancy.

Other causes of anemia during pregnancy typically include nutritional deficiencies resulting in impaired red blood cell production. In addition, inherited mutations of hemoglobin structure, known as hemoglobinopathies, or conditions resulting in increased destruction of red blood cells can also be a cause of anemia during pregnancy.

Given the potential for blood loss at delivery, which will worsen a preexisting anemia, it is important to identify and treat anemia during pregnancy to prevent adverse maternal and fetal outcomes. Consequently, universal screening of all pregnant patients for anemia should be done during the first and second trimesters.

Your first step is to perform a universal screening of your pregnant patient for anemia at their first prenatal visit.

Keep in mind that some patients may not have received their prenatal care, so they may present with a chief concern suggesting anemia in pregnancy. Start by obtaining a focused history and physical exam. And since anemia is diagnosed based on hemoglobin values, a CBC is essential. Additionally, as part of universal screening, all patients should be screened for hemoglobinopathies using hemoglobin electrophoresis at the start of their pregnancy, unless they have had prior testing. A positive family history of hemoglobinopathy increases their risk of having one too. This is important because any patient with a hemoglobinopathy is at risk for anemia due to the abnormal hemoglobin structure resulting in defective hemoglobin molecules.

Other important risk factors include malabsorptive conditions, restrictive diets, or even pica, which is a craving to consume non-food items like starch, dirt, or ice, and can lead to anemia from inadequate folate, vitamin B12, and iron.

You may notice symptoms like fatigue or restless legs. Now, when it comes to the physical exam, a mild increase in heart rate of 10 to 15 beats per minute is normal during pregnancy; but if the patient is anemic, it might reveal tachycardia. Sometimes, you may see pallor or atrophic glossitis, where the tongue appears smooth and glossy with a red or pink background. You may also notice ataxia, which is a lack of balance or coordination.

Next, assess which trimester your patient is in and take a look at their CBC. For patients in the first or third trimester, a hemoglobin less than 11 g/dL is diagnostic of anemia; whereas, for patients in the second trimester, a hemoglobin of less than 10.5 g/dL is diagnostic of anemia.

Here is a high yield fact! A hemoglobin level less than 6 g/dL is considered a severe anemia. This low level is associated with abnormal fetal oxygenation which can lead to fetal demise. If your patient's hemoglobin is less than 6 g/dL, assess the fetal status and proceed with maternal transfusion of packed red blood cells.

Let's get back to patients who are anemic but without such a drastically low hemoglobin. For these patients you will use the mean corpuscular volume, or MCV, to guide your work up. Determining the exact cause will then tailor your management. When the MCV is below 80 femtoliters, this is considered a microcytic anemia.

To find the cause of a microcytic anemia, you should obtain labs, such as iron studies, which include ferritin, serum iron level, transferrin saturation, and serum total iron binding capacity, known as TIBC. If ferritin, serum iron, and transferrin saturation are low, and TIBC is high, then your diagnosis is iron deficiency anemia, which is actually the most common cause of microcytic anemia in pregnancy.

Here is a clinical pearl! While an entire iron panel is ordered and interpreted, ferritin is the most sensitive test for iron deficiency. In patients with early iron deficiency, ferritin may be the only abnormal lab.

Okay, let's talk about treatment for iron deficiency anemia,

Start with oral iron supplementation. Advise the patient to take one iron tablet three days per week, such as Monday, Wednesday, and Friday, since evidence suggests daily supplementation can limit absorption. Also, taking the iron on an empty stomach and with vitamin C, can maximize absorption. However, keep in mind that some patients may develop gastrointestinal side effects like nausea and vomiting. If your patient can't tolerate iron on an empty stomach, they may take it with food or right after meals.

After about a month of oral iron supplementation, repeat the CBC, and assess the response. If the hemoglobin has risen by a point, this suggests an adequate response and they can continue with oral iron. However, if hemoglobin doesn't improve significantly, there is an inadequate response. If this is the case, switch the patient from oral to IV iron supplementation.

Here's another clinical pearl! For anemic patients who cannot tolerate oral iron, have a known malabsorptive condition, or are severely iron deficient with a ferritin below 12, it is reasonable to go directly to IV iron without a trial of oral replacement.

Finally, let's take another look at iron studies. If the patient with microcytic anemia has normal ferritin, or normal iron studies, you should consider an alternative diagnosis, such as hemoglobinopathies or thalassemia, respectively.