Abstract
Study question
Is maternal cell-free DNA (cfDNA) testing a feasible alternative to the analysis of the product of conception (POC) in clinical miscarriages?
Summary answer
This study demonstrates that genome-wide cfDNA testing in the maternal bloodstream constitutes a reliable tool to analyse chromosome aneuploidies in clinical miscarriages.
What is known already
It is well established that 50-70% of clinical miscarriages are caused by numerical chromosomal anomalies (aneuploidies), mostly trisomies. To date, conventional cytogenetic and advanced molecular techniques are used for the analysis of POC to identify the genetic cause of miscarriage, providing valuable information for genetic counselling. However, both approaches are based in the direct analysis of the abortive tissue, which entails several limitations due to the risk of culture failure and/or maternal cell contamination. To solve these drawbacks, maternal cfDNA testing emerges as a promising alternative due to the accumulated evidence.
Study design, size, duration
This was a retrospective study conducted in a reference genetic laboratory from January to December 2020. Before carrying out the foetal tissues collection that precludes the POC analysis, a blood sample was drawn to evaluate possible aneuploidies by cfDNA testing. Using NGS+STR POC results as the gold standard, results derived from both studies were compared to assess the percentage of concordance and the cases of non-informativeness (foetal fraction (FF) <2%), false positives, and false negatives.
Participants/materials, setting, methods
A total of 12 cases were included in the study. cfDNA testing in the mother’s blood was performed by using Illumina’s technology platform. Genetic testing for POC was done using an NGS technology (Thermo Fisher Scientific, USA) for 24 chromosome aneuploidy screening. Short-tandem repeat (STR) analysis allowed us to detect or rule out maternal cell contamination (MCC) and some types of polyploidies.
Main results and the role of chance
The non-informative rate for both analysis techniques was 9.1% (1 out of 12 cases: 1 low FF for cfDNA testing and maternal cell contamination for POC analysis). The median cfDNA FF was 9.0%. Using the molecular POC analysis as gold standard, the concordance rate between both studies was 90.0% (9 out of 10 cases;1 monosomy X, 1 trisomy (T) 21, 1 T22, 1 T11 and 5 patients with no alteration detected). No mosaics or structural rearrangements were identified by either of the two analysis techniques. The only discordant result was a case in which cytogenetics of POCs identified a triploidy. This discordancy is expected since triploidies are outside the scope of cfDNA testing. Also, foetal sex was correctly assigned in all informative cases. The sensibility and specificity of the study were estimated at 80.0 (4/5) and 100.0% (6/6), respectively. Statistics analysis suggested that no significant difference was found between both techniques regarding the aneuploidy detection ability (P=0.5). These promising results indicate that genome-wide cfDNA-based screening provides a non-invasive approach for determining whether foetal aneuploidy could explain the loss in patients experiencing early o recurrent pregnancy loss (RPL).
Limitations, reasons for caution
The sample size prevents drawing more significant conclusions regarding the diagnosis power similarity between both testing techniques. Therefore, a larger cohort will be essential to improve confirm the cfDNA testing performance. Current cfDNA testing technology fails in polyploidy identification, which is a potential cause of pregnancy loss.
Wider implications of the findings
CfDNA testing could be an alternative to POC analysis in clinical miscarriage. If optimized, cfDNA testing could be used contingently with the molecular POC analysis in cases where maternal cell contamination is present. As a result, the overall success rate in the POC program could be substantially improved.
Trial registration number
NA
COVID-19 salivary signature: diagnostic and research opportunities
