Aneuploidy screening: what test should I use?

Screening for the risk of fetal aneuploidy can be effectively performed in either the first or second trimester. When obtained independently, the interpretation of those data is straightforward. However, the effectiveness of screening can be enhanced by combining studies performed in each trimester in a variety of ways. In this commentary we will define and discuss both the advantages and disadvantages of using integrated, stepwise, sequential or contingency screening for risk assessment of fetal aneuploidy.