Noninvasive prenatal detection and selective analysis of cell-free  DNA obtained from maternal blood:  evaluation for trisomy 21 and trisomy 18

Selective analysis of cell-free DNA in maternal blood for evaluation of fetal trisomy

Chromosome-selective sequencing of maternal plasma cell-free DNA for first-trimester detection of trisomy 21 and trisomy 18.

Incorporating First-Trimester Down Syndrome Studies Into Prenatal Screening

Comparing Three Screening Strategies for Combining First-and Second-Trimester Down Syndrome Markers

Screening for Fetal Chromosomal Abnormalities

 First Trimester Diagnosis and Screening for Fetal Anueploidy

First and Second Trimester Antenatal Screening for Down's Syndrome:  The Results of the Serum, Urine and Ultrasound Screening Study (SURUSS)