The performance of cfDNA testing for trisomy 21 in twin pregnancy is similar to that reported in singleton pregnancy and is superior to that of the first-trimester combined test or second-trimester biochemical testing.
Cell-free DNA (cfDNA) testing, which involves analyzing fetal DNA in a maternal blood sample, is a non-invasive and highly accurate test for Down syndrome in singleton pregnancy, but its effectiveness in twin pregnancy has been unclear. A new analysis by Gil and Nicolaides et al. reveals that cfDNA testing for Down syndrome in twins is just as effective as in singletons, with a detection rate of 98% and only a 0.05% rate of misdiagnosis.
The analysis combined information from a dataset of 997 twin pregnancies in addition to results from seven previously published studies. The study also found that cfDNA testing for trisomy 21 in twin pregnancy is superior to that of the first-trimester combined test or second-trimester biochemical testing. The number of cases of trisomies 18 and 13 was too small to allow accurate assessment of the predictive performance of the cfDNA test for these trisomies.
In many countries, including the United States, cfDNA testing is not recommended for use in twin pregnancy. These latest findings provide compelling evidence that mothers carrying twins should not be denied this safe and effective test.
According to Anthony Odibo, Editor in Chief of Ultrasound in Obstetrics & Gynecology: “The introduction of maternal serum cell free DNA (cfDNA) analysis in screening for aneuploidy is arguably one of the most significant breakthroughs in prenatal screening and diagnosis in the past 10 years. Use of cfDNA for aneuploidy screening is now of care for singleton gestations. With twin pregnancies, several organizations in USA have not endorsed using cfDNA for aneuploidy screening. The controversy stems from an inability to ascertain the exact contribution of each fetus to the fetal fraction of cfDNA in the maternal circulation. Investigations have focused on providing reliable data on the role of cfDNA in twins and higher order gestations. The latest meta-analysis from The Fetal Medicine Foundation indicates that the performance of cfDNA testing for trisomy 21 in twin pregnancies is similar to that reported in singleton pregnancies and is far superior to that of the non-cfDNA-based screening tests currently used.”
The implications of this research are that in a population of 1000 women with twin pregnancy undergoing screening for Down syndrome, using conventional biochemical testing, 50 would be told that they are at risk and would be recommended to have an invasive procedure. Using cfDNA testing, only one woman would be considered at risk, dramatically reducing the requirement for invasive testing and associated risk of miscarriage.