The Red Cell Distribution Width (RDW) test is a standard part of the Complete Blood Count (CBC) performed during initial prenatal screening. This simple blood test measures the variation in size among circulating red blood cells. An elevated RDW level in pregnancy signals an underlying issue that could affect both the mother’s health and the developing fetus, requiring further medical investigation.
Understanding Red Cell Distribution Width (RDW)
The RDW is a numerical value, typically expressed as a percentage, that quantifies the uniformity of red blood cell size. When red blood cells vary greatly in volume, a condition known as anisocytosis, the RDW value is high. For non-pregnant adults, the RDW reference range is often below 14.5%.
During pregnancy, a slight increase in RDW is a normal physiological adaptation due to increased blood volume and rapid cell production. The upper limit of the normal range can extend up to 14.9% in the first trimester and up to 16.6% in the third trimester. A result is considered concerning when it rises significantly above these trimester-specific upper limits, indicating a pathological process rather than normal adaptation.
Underlying Conditions Indicated by Elevated RDW
An elevated RDW is a non-specific marker pointing toward a problem with red blood cell production or survival. The most frequent cause of a high RDW in pregnancy is nutritional deficiency, especially iron, folate, or Vitamin B12 deficiency. Insufficient levels of these nutrients disrupt the bone marrow’s ability to create appropriately sized red blood cells, resulting in a mix of differently sized cells that drives the RDW up.
The RDW can also serve as an early indicator of systemic stress or inflammation. Chronic inflammatory states, such as those caused by underlying infections or certain autoimmune conditions, can suppress normal red blood cell maturation. This leads to a heterogeneous population of cells and an increased RDW, often rising before other markers of anemia, such as hemoglobin, drop significantly. Less common causes include hemoglobin disorders like thalassemia, which inherently cause variations in cell size.
Specific Maternal and Fetal Risks
The danger of an elevated RDW in pregnancy lies in its strong correlation with serious adverse outcomes, even when the mother does not have severe anemia. A high RDW is a recognized predictor for hypertensive disorders, particularly preeclampsia, which is characterized by high blood pressure and organ damage. RDW values are significantly higher in women who develop preeclampsia compared to healthy pregnant women, and the level is linked to the severity of the condition. High RDW is also associated with an increased risk of other complications, including gestational diabetes and intrahepatic cholestasis of pregnancy.
Fetal Outcomes
For the fetus, the risks are tied to the underlying maternal condition. High RDW is linked to adverse outcomes like fetal growth restriction (FGR) and preterm birth. FGR occurs when the fetus does not grow at the expected rate, often due to placental issues. A sudden rise in RDW has been cited as a potential biomarker for an increased risk of preterm labor.
Clinical Management and Follow-Up
An elevated RDW result prompts a focused clinical investigation to determine the exact cause. This usually involves further specific blood work, including measurements of serum iron, ferritin, Vitamin B12, and folate levels, to pinpoint the specific nutritional deficiency that is driving the abnormal RDW.
Management is tailored to treat the underlying cause, often involving targeted supplementation. If a deficiency is identified, high-dose supplements (iron, B12, or folate) are prescribed. For suspected inflammation, healthcare providers work to manage the underlying chronic condition. Regular monitoring of the RDW and other complete blood count parameters is important to ensure the intervention is effective and maternal and fetal well-being is maintained.