Fetal Cell Screen Health Article

Definition

The fetal cell screen is a procedure performed during pregnancy whereby blood is drawn from the mother and examined for the presence of fetal cells.

Purpose

The fetal cell screen is used to assess the degree of Rh (also called Rho [D] or D) sensitization in an Rh-negative mother during gestation of an Rh-positive fetus. Fetal red cells carrying the Rh positive antigen can leak into the maternal circulation and immunize the Rh-negative mother, possibly leading to hemolytic disease of the newborn. The potential degree of isoimmunization and severity of hemolytic disease increases with each Rh-incompatible pregnancy. The fetal cell screen quantifies the extent of the leakage and permits determination of how much Rh immune globulin (RhoGAM) to administer in order to prevent the mother from developing anti-D antibodies against the fetus.

Rho immune globulin is normally administered by intramuscular injection to Rh-negative mothers at 28-30 weeks of gestation and again within 72 hours postpartum. The dosage is higher for mothers who test positive for fetal red blood cells. The treatment is performed earlier when amniocentesis or chorionic villus sampling is performed, or following spontaneous or elective abortion.

Aside from Rh-incompatibility cases, the test may be ordered to investigate the severity of maternal-fetal hemorrhage following a trauma, or during post-mortem examination of a stillbirth.

Precautions

Although in principle the fetal cell screen is simple to perform, the procedure is subjective, labor-intensive, and time-consuming; and requires skill, experience, and strict attention to detail.

When possible, the procedure should be scheduled with the laboratory in advance. The specimen may be rejected by the laboratory if it is delivered too long after being drawn; or if clotted, hemolyzed, or contaminated with heparin (as may happen when drawn at the same time as a sample for blood gases).

The possibility that the mother has an inherited blood disorder that might produce fetal hemoglobin should be considered when interpreting a positive result.