In a paper published earlier this year in the British Medical Journal, Dr. Lo and his co-researchers showed they could find all 86 cases of Down syndrome in testing done on 752 pregnant women.

WSJ: New Prenatal Tests Offer Safer, Early Screenings

At the time, Verinata's testing materials claimed 100% sensitivity in detecting Down syndrome.

WSJ: New Questions on Cutting-Edge Prenatal Tests

Verinata, Illumina's testing unit, incorrectly cleared a New York woman's fetus of Down syndrome, according to the case report presented at a medical society meeting last month.

WSJ: New Questions on Cutting-Edge Prenatal Tests

In her lab, Dr. Cherry said she had found four out of six positive results for Trisomy 18, or Edwards syndrome, which the tests also detect, appeared to be false alarms after follow-up testing.

WSJ: New Questions on Cutting-Edge Prenatal Tests