Aneuploidy Screening Using Noninvasive Prenatal Testing in Twin Pregnancies

Objectives To describe experience with noninvasive prenatal testing (NIPT) in twins. Methods For clinical study A, 115 maternal blood samples from twin pregnancies with known clinical outcomes were analyzed. Classifications for chromosomes 13, 18, 21, X, and Y were compared with fetal karyotypes from invasive prenatal procedures and/or newborn physical examinations. In addition, 487 clinical samples from twin pregnancies were submitted for NIPT (clinical study B), with outcomes requested from providers. Results In clinical study A, all 115 samples were correctly classified: 3 of 3 trisomy 21 (one affected fetus), 1 of 1 monochorionic trisomy 18, and 111 euploid. Clinical study B included 487 clinical twin samples, of which a result was reported for 479 (98.4%), with aneuploidy detected/suspected in nine (1.9%): seven trisomy 21 cases detected, one trisomy 21 suspected, and one with trisomy 21 detected and trisomy 18 suspected. Information on aneuploidy outcomes was available for 171 (35.7%) cases in clinical study B. Of the nine aneuploidy detected/suspected cases, six of the aneuploidy detected cases were confirmed to be true positives in at least one twin based on karyotype or birth outcome, and two were suspected to be concordant based on ultrasound findings; the one known discordant result was for the aneuploidy suspected case. No false negatives were reported. Conclusions NIPT performed well for trisomy 21 in twin gestations with a combined trisomy 13, trisomy 18, and trisomy 21 false-positive frequency of 0% for clinical study A and 0.2% for clinical study B.