Mean Diameter of Fetal Red Blood Cells (Fetal Hemoglobin Profile)

What This Test Measures

The test evaluates the mean diameter of fetal red blood cells (RBCs). RBCs are the cells in your blood that carry oxygen. In fetal blood, these cells may differ slightly from those in adult blood due to the presence of fetal hemoglobin. Measuring their size helps healthcare providers examine how well your baby’s blood is functioning.

Why It Might Be Ordered

A healthcare provider may order this test if there are concerns about fetal blood health, such as suspected anemia, hemolytic disease of the fetus and newborn (HDFN), or other blood-related conditions. It could also be part of a broader evaluation if you have a history of complications during pregnancy or if certain genetic or chromosomal conditions are suspected.

Sample Collection and Preparation

This test requires a small sample of fetal blood, typically obtained through procedures like amniocentesis or cordocentesis. The blood is collected in a sterile tube and sent to a lab for analysis. The lab will measure the average diameter of fetal RBCs using advanced imaging or flow cytometry techniques.

What to Expect Before the Test

Before the test, you may receive mild sedation or anesthesia to ensure comfort. The procedure itself involves inserting a needle into the amniotic sac or directly into the fetal circulation. You may experience mild cramping or discomfort, but it is generally well-tolerated. Rest and hydration are often recommended afterward.