Components of Maternal Blood

Current prenatal screening tests include the measurement of certain maternal blood proteins that have been shown to be reliable indicators of fetal abnormalities.

Fetal cells and fetal cell-free nucleic acid (RNA and DNA) account for rare but significant components of maternal blood when considered in the context of prenatal testing.

Fetal nucleated red blood cells are of particular importance, due to the fact that they contain a complete representation of the entire fetal genome and, if isolated, can provide the best opportunity for comprehensive prenatal testing. And although some fetal cell types have been shown to survive in maternal circulation for years following a pregnancy, fetal nucleated red blood cells are relatively short-lived in the maternal circulation, leaving no risk that these fetal cells are from a previous pregnancy.

Fetal cell-free nucleic acids are also a potential source of genetic material for use in prenatal testing. Fetal cell-free DNA is especially interesting because once isolated from maternal blood, DNA is a relatively stable molecule, making it easy to handle, transport and store. In addition, it was recently shown that isolated cell-free DNA from maternal blood can be analyzed by shotgun sequencing to accurately detect the presence of fetal aneuploidy.³

3. Fan HC, Blumenfeld YJ, Chitkara U, Hudgins L, Quake SR. Noninvasive diagnosis of fetal aneuploidy by shotgun sequencing DNA from maternal blood. Proc Natl Acad Sci USA. 2008 Oct 21;105(42):16266-16271.

Components found in maternal blood

	Nucleated red blood cells (nRBCs) - These cells represent immature red blood cells and are seen at higher concentrations in utero and in newborns than in adults. Fetal nRBCs are also found at very low concentrations in the maternal circulation.
	White blood cells - These represent the cells of the maternal immune system.
	Cell-free DNA - This DNA is thought to be a normal byproduct of cellular breakdown and processing, and is a typical element of human blood. Maternal blood contains cell-free DNA from both the mother and the fetus.
	Cell-free RNA - This single-stranded mRNA, thought to be a normal byproduct of cellular breakdown and processing, is a typical but fragile element of human blood. Maternal blood contains cell-free RNA from both the mother and the fetus.
	Plasma Proteins - All human blood contains varying levels of proteins that, in pregnancy, can serve as markers for prenatal screening tests.
	Trophoblasts - These cells originate from the placenta and are found in very low concentrations in the maternal blood circulation.