A dPCR-NIPT assay for detections of trisomies 21, 18 and 13 in a single-tube reaction-could it replace serum biochemical tests as a primary maternal plasma screening tool?

BACKGROUND: The next generation sequencing (NGS) based non-invasive prenatal test (NIPT) has outplayed the traditional serum biochemical tests (SBT) in screen of fetal aneuploidies with a high sensitivity and specificity. However, it has not been widely used as a primary screen tool due to its high cost and the cheaper SBT is still the choice for primary screen even with well-known shortages in sensitivity and specificity. Here, we report a multiplex droplet digital PCR NIPT (dPCR-NIPT) assay that can detect trisomies 21, 18 and 13 (T21, T18 and T13) in a single tube reaction with a better sensitivity and specificity than the SBT and a much cheaper price than the NGS-NIPT. METHODS: In this study, the dPCR-NIPT assay's non-clinical characteristics were evaluated to verify the cell free fetal DNA (cffDNA) fraction enrichment efficiencies, the target cell free DNA (cfDNA) concentration enrichment, the analytical sensitivity, and the sample quality control on the minimum concentration of cfDNA required for the assay. We validated the clinical performance for this assay by blindly testing 283 clinical maternal plasma samples, including 36 trisomic positive samples, from high risk pregnancies to access its sensitivity and specificity. The cost effectiveness of using the dPCR-NIPT assay as the primary screen tool was also analyzed and compared to that of the existing contingent strategy (CS) using the SBT as the primary screen tool and the strategy of NGS-NIPT as the first-tier screen tool in a simulating situation. RESULTS: For the non-clinical characteristics, the sample processing reagents could enrich the cffDNA fraction by around 2 folds, and the analytical sensitivity showed that the assay was able to detect trisomies at a cffDNA fraction as low as 5% and the extracted cfDNA concentration as low as 0.2 ng/µL. By testing the 283 clinical samples, the dPCR-NIPT assay demonstrated a detection sensitivity of 100% and a specificity of 95.12%. Compared to the existing CS and the NGS-NIPT as the first-tier screen strategy, dPCR-NIPT assay used as a primary screen tool followed by the NGS-NIPT rescreen is the most economical approach to screen pregnant women for fetal aneuploidies without sacrificing the positive detection rate. CONCLUSION: This is the first report on a dPCR-NIPT assay, consisting of all the necessary reagents from sample processing to multiplex dPCR amplification, can detect T21, T18 and T13 in a single tube reaction. The study results reveal that this assay has a sensitivity and specificity superior to the SBT and a cost much lower than the NGS-NIPT. Thus, from both the test performance and the economic benefit points of views, using the dPCR-NIPT assay to replace the SBT as a primary screen tool followed by the NGS-NIPT rescreen would be a better approach than the existing CS for detection of fetal aneuploidies in maternal plasma.

Cesarean Section or Vaginal Delivery to Prevent Possible Vertical Transmission From a Pregnant Mother Confirmed With COVID-19 to a Neonate: A Systematic Review.

Background: The impact of delivery mode on the infection rates of Coronavirus disease 2019 (COVID-19) in the newborn remains unknown. We aimed to summarize the existing literature on COVID-19 infection during pregnancy to evaluate which mode of delivery is better for preventing possible vertical transmission from a pregnant mother confirmed with COVID-19 to a neonate. Methods: We performed a comprehensive literature search of PubMed, Embase, Cochrane Library, Web of Science, Google Scholar, and the Chinese Biomedical Literature database (CBM) from 31 December 2019 to 18 June 2020. We applied no language restrictions. We screened abstracts for relevance, extracted data, and assessed the risk of bias in duplicate. We rated the certainty of evidence using the GRADE approach. The primary outcome was severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test positivity in neonates born to mothers with confirmed COVID-19 following different delivery modes. Secondary outcomes were neonatal deaths and maternal deaths. This study is registered with PROSPERO, CRD42020194049. Results: Sixty-eight observational studies meeting inclusion criteria were included in the current study, with no randomized controlled trials. In total, information on the mode of delivery, detailed neonatal outcomes, and SARS-CoV-2 status were available for 1,019 pregnant women and 1,035 neonates. Six hundred and eighteen (59.71%) neonates were born through cesarean section and 417(40.29%) through vaginal delivery. Probable congenital SARS-CoV-2 infections were reported in 34/1,035 (3.29%) neonates. Of babies born vaginally, 9/417 (2.16%) were tested positive compared with 25/618 (4.05%) born by cesarean. Of babies born vaginally, 0/417 (0.00%) neonatal deaths were reported compared with 6/618 (0.97%) born by cesarean. Of women who delivered vaginally, 1/416 (0.24%) maternal deaths were reported compared with 11/603 (1.82%) delivered by cesarean. Two women died before delivery. Sensitivity analyses and subgroup analyses showed similar findings. Conclusions: The rate of neonatal COVID-19 infection, neonatal deaths, and maternal deaths are no greater when the mother gave birth through vaginal delivery. Based on the evidence available, there is no sufficient evidence supporting that the cesarean section is better than vaginal delivery in preventing possible vertical transmission from a pregnant mother confirmed with COVID-19 to a neonate. The mode of birth should be individualized and based on disease severity and obstetric indications. Additional good-quality studies with comprehensive serial tests from multiple specimens are urgently needed. Study registration: PROSPERO CRD42020194049.