ACOG Practice Bulletin No. 77: screening for fetal chromosomal abnormalities.

In the last decade, numerous markers and strategies for Down syndrome screening have been developed. Algorithms that combine ultrasound and serum markers in the first and second trimesters have been evaluated. Furthermore, the practice of using age cutoffs to determine whether women should be offered screening or invasive diagnostic testing has been challenged. The purpose of this document is to 1) present and evaluate the best available evidence for the use of ultrasonographic and serum markers for selected aneuploidy screening in pregnancy and 2) offer practical recommendations for implementing Down syndrome screening in practice.