Performance of screening for aneuploidies by cell-free DNA analysis of maternal blood in twin pregnancies.

OBJECTIVES: To report clinical implementation of cell-free DNA (cfDNA) analysis of maternal blood in screening for trisomies 21, 18 and 13 in twin pregnancies and examine variables that could influence the failure rate of the test. METHODS: cfDNA testing was performed in 515 twin pregnancies at 10-28 weeks' gestation. The failure rate of the test to provide results was compared with that in 1847 singleton pregnancies, and logistic regression analysis was used to determine which factors among maternal and pregnancy characteristics were significant predictors of test failure. RESULTS: Failure rate of the cfDNA test at first sampling was 1.7% in singletons and 5.6% in twins. Of those with a test result, the median fetal fraction in twins was 8.7% (range, 4.1-30.0%), which was lower than that in singletons (11.7% (range, 4.0-38.9%)). Multivariable regression analysis demonstrated that twin pregnancy, higher maternal weight and conception by in-vitro fertilization provided significant independent prediction of test failure. Follow-up was available in 351 (68.2%) of the twin pregnancies and comprised 334 with euploid fetuses, 12 discordant for trisomy 21 and five discordant for trisomy 18. In all 323 euploid cases with a result, the risk score for each trisomy was < 1:10 000. In 11 of the 12 cases with trisomy 21 and in the five with trisomy 18, the cfDNA test gave a high-risk result, but in one case of trisomy 21, the score was < 1:10 000. CONCLUSION: In twin pregnancies screening by cfDNA testing is feasible, but the failure rate is higher and detection rate may be lower than in singletons.

The first 3,000 Non-Invasive Prenatal Tests (NIPT) with the Harmony test in Belgium and the Netherlands.

As the classical first trimester Down syndrome screening (FTS, combination test) has a false-negative rate of 20-25% and > 95% of the abnormal FTS results are false-positive, we evaluated the new Non-Invasive Prenatal Test (NIPT) in Belgium and the Netherlands. The study population consisted of 3000 consecutive pregnancies in Belgium and the Netherlands in which NIPT was performed using the Harmony test. In 57 (1.9%) of the 3000 pregnancies an abnormal NIPT result was found. This included 51 fetuses with trisomy 21, 4 fetuses with trisomy 18 and 2 fetuses with trisomy 13. In 47 of the 57 the NIPT result was confirmed by genetic testing of material obtained by amniocentesis or chorionic biopsy, and no false-positive results were recorded. The false-negative rate as determined on more than 2000 women that had delivered at the time of reporting was low, and so far only 2 false-negative results were reported (one trisomy 18 and one trisomy 21). The failure rate where no NIPT result could be obtained after repeated sampling was 0.90%. In this large clinical series, NIPT using the Harmony test proves to be a very reliable prenatal test to detect fetal trisomies 21, 18 and 13 in maternal blood in Belgium and the Netherlands.