First results of fetal chromosome aneuploidy testing using cell-free DNA in Lithuania

Abstract

Backround. Circulating free DNA (fDNA) in blood of pregnant women is a mixture of genomic DNA of maternal and fetal origin. When applying the right method its analysis helps to detect fetal chromosomal aneuploydies with high sensivity and low fals positive rates. Methods. Retrospective study of 80 singleton pregnancies between 9 and 20 weeks. Maternal blood was collected at Alfa Clinic (Vilnius) and send to Natera (San Carlos CA USA). cfDNA was isolated from maternal plasma, and targeted multiplex PCR amplification followed by sequencing of 19[[unable to display character:  ]]488 polymorphic loci covering chromosomes 13, 18, 21, X, and Y was performed. Sequencing data were analyzed using the NATUS algorithm that determines the copy number for each of the five chromosomes tested. Results. Results were provided for 79 (98.8%) of the 80 cases. Most cases were in high risk pregnancy group (advanced maternal age and abnormal serum screening). Three cases were correctly identified as aneuploid, including trisomy 21 , trisomy 18 and rare case of mosaic case of X monosomy, with no false positive results. Test specificity showed 99% (CI 98-99.9 %) efficancy because all cases were confirmed by amniocentesis. One case was with low fetal fraction (2.3 %), however because of abnormal serum screening (very low PAPP-A and free beta-hCG) ammniocentesis and cyrtogenetic analysis was performed that revealed triploidy 69 XXY. Conclusions. cfDNA testing in maternal blood using targeted sequencing of polymorphic loci at chromosomes 21, 18 and X showed accurate detection of fetal autosomal aneuploidies including chromosomal mosaicism. It helped to reduce the need of unnecessary invasive procuderes (CVS and amniocentesis).