" Let’s say you are 31 and you undergo the cell-free fetal DNA screening. With a good result on this, the baby’s risk of having Down syndrome is around 1 in 100,000. The risk of miscarriage from the amniocentesis or CVS test is around 1 in 800. What you need to decide for yourself is whether having a baby with Down syndrome unexpectedly would be more than 125 times worse than having a miscarriage (that is, 100,000 divided by 800). If yes, then skip right to the invasive test—probably CVS given the timing. If no, then stick with the noninvasive screen. "

― Emily Oster , Expecting Better: Why the Conventional Pregnancy Wisdom is Wrong - and What You Really Need to Know