Aneuploidy screening by non-invasive prenatal testing in twin pregnancy

Objectives To describe our experience with non-invasive prenatal testing (NIPT) in twin pregnancy. Methods Two sets of maternal blood samples from twin pregnancies were analyzed at our laboratory using NIPT: 115 stored samples from pregnancies with known outcome (Clinical Study A) and 487 prospectively collected samples for which outcomes were requested from providers (Clinical Study B). NIPT was used to screen for the presence of fetal aneuploidy on chromosomes 13, 18, 21, X and Y in all cases, and results were compared with outcomes when known. Results In Clinical Study A, all 115 samples were classified correctly by NIPT: three cases of trisomy 21 (one fetus affected), one of monochorionic trisomy 18 (both fetuses affected) and 111 euploid. In Clinical Study B, a NIPT result was reported for 479 (98.4%) of the 487 samples. Aneuploidy was detected or suspected in nine (1.9%) cases: seven cases of trisomy 21 detected, one case of trisomy 21 suspected and one case with trisomy 21 detected and trisomy 18 suspected. Information on aneuploidy outcome was available for 171 (35.7%) cases in Clinical Study B. Of the nine cases with aneuploidy detected or suspected, six were confirmed to be a true positive 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. Conclusion NIPT performed well in the detection of trisomy 21 in twin pregnancy, with a combined false-positive frequency for trisomies 13, 18 and 21 of 0% for Clinical Study A and 0.2% for Clinical Study B. (C) 2016 Illumina. Ultrasound in Obstetrics& Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.