Diagnostic accuracy of cell‐free DNA in maternal blood in detecting chromosomal anomalies in twin pregnancies: systematic review and meta‐analysis

Objectives: To report the diagnostic accuracy of cell-free DNA (cfDNA) in maternal blood in detecting chromosomal anomalies in twin pregnancies. Methods: Medline, Embase and Cochrane databases were searched. The inclusion criteria were twin pregnancies undergoing cfDNA screening for Trisomies 13, 18, 21, monosomy X0 and other sex chromosomal anomalies (SCA). The index test was represented by a positive results of cfDNA test. The reference standard was represented by the karyotype results (obtained either pre or postnatally) or, in case of negative cfDNA result, by a normal neonatal phenotype. The quality of the studies was assessed using the revised tool for the quality assessment of diagnostic accuracy studies (QUADAS-2). Summary estimates of sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-) and diagnostic odds ratio (DOR), with the corresponding 95% Confidence Intervals (95% CI), were computed using the bivariate random-effects model. Results: Thirty-five studies were included. cfDNA had an overall high accuracy in detecting Trisomy 21 in twin pregnancies with a sensitivity of 98.8% (95% CI 96.5-100), a specificity of 100% (95% CI 99.9-100). Sensitivity and specificity were of 94.9% (95% CI 75.6-99.1) and 100 (95% CI 99.9-100) for Trisomy 18, and 84.6% (95% C% 54.6-98.1) and 100% (95% CI 99.9-100) for Trisomy 13 . We could not compute the diagnostic accuracy of cfDNA in detecting monosomy X0 in twins, while cfDNA had a sensitivity of 100% (95% CI 71.5-100) and a specificity of 99.8% (95% CI 99.7-99.9) in detecting other SCA (11 cases). The accuracy of cfDNA in detecting Trisomy 21, 18 and 13 was similar in dichorionic and monochorionic twin pregnancies. Conclusion: cfDNA has a high diagnostic accuracy in detecting Trisomy 18 and 21 in twin pregnancies, irrespective of chorionicity. Accuracy in the detection of Trisomy 13 and SCA was limited by the small number of affected cases and the difficulties in the confirmation of false negative cases in case of SCA and requires confirmation in larger studies.