Results of a prospective study combined with a meta-analysis suggest that cell-free DNA (cfDNA) testing for trisomy 21 (Down syndrome) may be just as effective in twin pregnancies as in singletons. The research also showed that in twin pregnancies, the noninvasive testing is superior to use of combined testing in the first trimester or second-trimester biochemical testing.
Published in Ultrasound in Obstetrics and Gynecology, the findings are from a prospective study and meta-analysis by European authors. They sought to assess performance of cfDNA testing for trisomies 21, 18 and 13 in twin pregnancy.
The data for the prospective study were from screening at 10 +0 and 14 +1 weeks in 997 twin gestations in two groups. The first group were women who self-referred for screening to institutions in London or Brussels. The second group were women selected for cfDNA testing after routine first-trimester combined testing at one of two National Health Service hospitals in England.
The authors also performed a meta-analysis of peer-reviewed publications on clinical validation or implemental of cfDNA testing for trisomies 21, 18 and 13 in twin pregnancy. Assessment of the literature and results from the prospective study were combined to determine cfDNA test performance.
In the prospective study, the researchers found that cfDNA testing correctly classified 16 of the 17 cases of trisomy 21 (94.1%), nine of 10 cases of trisomy 18 (90.0%), and 962 of 968 cases without any trisomy (99.4%) without any of the trisomies. Combining data from seven relevant studies, the pooled weighted detection rate (DR) and false-positive rate (FPR) for trisomy 21 were 98.2% and 0.05%, respectively. For trisomy 18, the DR and FPR were 88.9% and 0.03%, respectively, and for trisomy 13, they were 66.7% and 0.19%, respectively.
There were too few cases of trisomies 18 and 13, the authors said, to accurately assess the predictive performance of cfDNA testing. For trisomy 21, they concluded that their results show that “performance of the cfDNA test is superior, both in terms of higher DR and substantially lower FPR, to that of the first-trimester combined test or second-trimester biochemical test” in twin pregnancy. Clinically, the authors said, the results are “particularly important in the case of dichorionic twins in which both the incidence of aneuploidy and the invasive procedure-related risk of pregnancy loss are increased compared to in singletons.”