Earlier this year Illumina, the maker of the world’s most widely used DNA sequencing machines, agreed to pay nearly half a billion dollars for Verinata, a startup in Redwood City, California, that has hardly any revenues. What Verinata does have is technology that can do something as ethically fraught as it is inevitable: sequence the DNA of a human fetus before birth.

Verinata is one of four U.S. companies already involved in a rapidly expanding market for prenatal DNA testing using Illumina’s sequencers. Their existing tests, all launched in the last 18 months, can detect Down syndrome from traces of fetal DNA found in a syringeful of the mother’s blood. Until now, detecting Down syndrome has meant grabbing fetal cells from the placenta or the amniotic fluid, procedures that carry a small risk of miscarriage.