Maternal serum analyte screening for fetal aneuploidy.

In the first and second trimesters, chemicals produced by the fetoplacental unit are measured to assess risks of fetal abnormalities. Consistent associations between levels of these proteins in such pregnancies enable these biomarkers to be used to calculate risk for Down syndrome and other chromosomal abnormalities in individual pregnancies. Special consideration may be required when assessing risk in multiple pregnancies and pregnancies achieved with infertility therapy.