The Effect of Freezing on Non-invasive Prenatal Testing

• Published in: Scientific reports Vol. 9; no. 1; p. 6962
• Main Authors: Xie, Xiaolei, Li, Fuguang, Tan, Weihe, Yin, Weiguo, Chen, Feiyan, Guo, Xiaoyan
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 06.05.2019; Nature Publishing Group UK
• Subjects: Adult; Aneuploidy; Cell-Free Nucleic Acids - blood; Cell-Free Nucleic Acids - genetics; China; Chromosome 21; Chromosome Disorders - blood; Chromosome Disorders - diagnosis; Chromosome Disorders - genetics; Chromosomes; Chromosomes, Human - genetics; Cryopreservation; Female; Freezing; Freezing - adverse effects; Genetic Testing - methods; Genetic Testing - standards; High-Throughput Nucleotide Sequencing; Humans; Laboratories; Male; Patau's syndrome; Plasma; Predictive Value of Tests; Pregnancy; Prenatal Diagnosis - methods; Success; Trisomy; China
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-42980-7

Plasma cryopreservation is unavoidable in China, due to technical specifications requiring storage of additional plasma at -80 degrees for three years. However, the effect of freezing on non-invasive prenatal testing (NIPT) is still uncertain. We collected 144 euploid pregnant samples, 22 on trisomy 21, 4 on trisomy 13, and 3 on trisomy 18, by massively parallel sequencing before and after freezing. Compared with the success rate of 100% of fresh samples, the detection success rates of trisomy 21, trisomy 13 and euploidy in frozen samples by NIPT were 95.45%, 75% and 95.14%, respectively. Of these, 9 cases of frozen sample sequencing failed, with 8 cases being due to high GC content. The chromosome 21 (chr21) z-value of the frozen trisomy 21 samples was lower than that of fresh samples. Meanwhile, freezing reduced the male positive foetal cell-free DNA (cfDNA) fraction, which was accompanied by an increase in the Unimap-GC level in the massively parallel sequencing data and a decrease in the Unique reads/Total reads ratio. Laboratory freezing reduced the chr21 z-value of foetal trisomy 21, which can be explained by a reduction in the foetal cfDNA fraction and effective Unique reads for NIPT analysis. The Unimap-GC content of the serum samples after freezing was higher, which can lead to failure of NIPT detection.